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Composite Structures
Journal Prestige (SJR): 1.905
Citation Impact (citeScore): 5
Number of Followers: 296  
 
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 0263-8223
Published by Elsevier Homepage  [3158 journals]
  • Damage model for predicting shear strength of carbon/carbon composite
           fastener based on post-failure behavior
    • Abstract: Publication date: 1 August 2019Source: Composite Structures, Volume 221Author(s): Faqi Liu, Zhidong Guan, Tianya Bian Fasteners made of carbon/carbon composites (C/Cs) have been developed for joining C/Cs components in high-temperature environment. A numerical damage model based on post-failure behavior was developed for simulating shear strength of 3D weave C/Cs fastener under several load angles. 3D pixel method was employed to simulate the heterogeneous damage process of constituents considering weave geometry in the macro model. Experiments were performed and the main damage as well as failure modes are also provided. It shows that the damage model can provide reasonable predictions compared to experiment data. And the damage mechanism observed in experiment can be reproduced in the numerical simulation. Furthermore, the effect of load angle on shear strength and failure modes was investigated which shows the strength of specimen decreases with increase of load angle. Numerical results showed different damage progression under several load angles which also reflected different load curve trends and post-failure behavior.
       
  • Analytical assessment of the stress-transfer mechanism in FRCM composites
    • Abstract: Publication date: 15 July 2019Source: Composite Structures, Volume 220Author(s): Pierluigi Colombi, Tommaso D'Antino Fiber reinforced cementitious matrix (FRCM) composites represent an effective alternative to fiber reinforced polymers (FRP) to strengthen existing concrete and masonry structures. When a single layer of fiber textile is employed, FRCMs generally failed due to debonding at the matrix-fiber interface and the presence of friction/interlocking residual stresses was observed for some composites. Therefore, the study of the stress-transfer mechanism is a fundamental topic to understand the behavior of FRCM composites and provide reliable design procedures. In this paper, the bond behavior of FRCM composites is studied by an analytical approach based on the use of an elasto-brittle bond-slip law that accounts for the possible presence of friction stresses. A stress and an energy criterion are put forward to describe the stress-transfer mechanism distinguishing between the bond and friction contributions. Finally, a comparison between the results of the analytical approach and corresponding experimental load responses is provided, showing that the methodology proposed is a fast and easy tool to estimate the bond behavior of FRCM composites.
       
  • A meso-mechanical model to simulate the tensile behaviour of Ultra-High
           Performance Fibre-Reinforced Cementitious Composites
    • Abstract: Publication date: Available online 24 April 2019Source: Composite StructuresAuthor(s): Amin Abrishambaf, Mário Pimentel, Sandra Nunes A simple model is proposed to predict the uniaxial tensile behaviour of ultra-high performance fibre-reinforced cementitious composites (UHPFRC) based on a meso-level description of the involved mechanics. The model relies on quantifiable material properties of the both matrix and fibres, on basic information concerning the fibre structure (such as fibre volumetric fraction, fibre orientation and geometry) and on three model parameters. Pullout tests on short fibres embedded in ultra-high performance cementitious matrix with different orientation angles and embedded lengths were developed for estimating the representative value of the average fibre-to-matrix bond-strength to be adopted, as well as for defining the fibre efficiency function describing the effects of fibre orientation on the pullout force. The model performance is validated against a series of uniaxial tensile tests on UHPFRC specimens covering a wide range of tensile behaviours. It is shown that the tensile response of UHPFRC can be well reproduced both in the hardening and softening stages with a single set of model parameters, and for a significant range of fibre contents and orientation profiles.
       
  • Optimization of composite dowels shape in steel-concrete composite floor
    • Abstract: Publication date: Available online 24 April 2019Source: Composite StructuresAuthor(s): Piotr Lacki, Przemysław Kasza, Konrad Adamus The paper contains a numerical analysis of a steel-concrete composite beam with a composite dowel. The connector is a contoured part of the web in a half of the steel section. In the first part of the work, the composite beam was analytically designed in accordance with PN-EN 1994-1-1 standard. Three cross-sections were selected from a hot-rolled sections 1/2 HEB 600, 1/2 HEA 500 and 1/2 HEA 400, so that the beams effort was 50%, 70% and 90% respectively. The length of the beam was 6.0 m. Structural steel S235, reinforcement steelfyk = 500 MPa (B500B) and concrete C20/25, C25/30, C30/37 were used. In the second part of the work the numerical analysis was carried out using the ADINA System program based on the Finite Element Method. The shape of the composite dowels in the class from the concrete class was optimized. The influence of the composite dowels shape on the stress concentration in the area of the composite dowels depending on the beam effort was considered. The stresses and displacements in the steel and concrete parts as well as cracking in concrete were assessed.
       
  • A new constitutive model for steel fibre reinforced concrete subjected to
           dynamic loads
    • Abstract: Publication date: 1 August 2019Source: Composite Structures, Volume 221Author(s): Lei Yang, Xiaoshan Lin, Huiyun Li, Rebecca J. Gravina The use of steel fibre reinforced concrete (SFRC) in protective structures has gained worldwide interest due to its superior mechanical characteristics. At present, hydrocode material models have been frequently used to simulate the dynamic behaviour of SFRC subjected to impact and blast loads. However, as these material models are developed for normal concrete, much effort is required for model calibration, and their other drawbacks, such as the neglect of shear dilation and the inappropriate consideration of strain-rate effect, may lead to inaccuracies in numerical predictions. In this study, a new constitutive material model is developed for SFRC, in which the damage evolution, shear dilation and strain-rate dependent material properties are properly taken into account. The new material model could accurately capture the mechanical behaviours of SFRC (i.e. strain hardening and softening in both compression and tension) with simple input parameters. It is then incorporated into the commercial finite element code LS-DYNA to simulate the structural behaviour of SFRC components under various loading conditions. The effectiveness and accuracy of the new material model are validated against the reported experimental results.
       
  • A combined strain and compliance method for improving ASTM D6671 to
           measure the mixed modes I/II interlaminar fracture toughness
    • Abstract: Publication date: 1 August 2019Source: Composite Structures, Volume 221Author(s): W. Xu, Z.Z. Guo, Y. Yu Mixed modes interlaminar delamination is one of the most common and serious failure modes in advanced carbon fiber reinforced composite materials. The ASTM standard D6671 is widely used to measure the mixed modes I/II interlaminar fracture toughness. One of the shortcomings of the current ASTM D6671 is the requirement of measuring the material Young’s moduli from separate tensile tests and samples, which are time-consuming and source of uncertainty. Accurate and closed-form strain and compliance solutions to the mixed mode bending specimen are given in this paper. By using these solutions, a combined strain and compliance method is proposed to measure the mixed modes I/II interlaminar fracture toughness, which avoids the measurement of the Young’s moduli from separate tests and specimens. The average difference between the mixed modes fracture toughness measured from the present method and that from ASTM D6671 is within 5%, thus the present paper provides a consistent and simple method for measuring the mixed modes I/II interlaminar fracture toughness.
       
  • Influence of restraint thermal effects on the bond strength of externally
           bonded CFRP-concrete joints
    • Abstract: Publication date: 1 August 2019Source: Composite Structures, Volume 221Author(s): Alessandro Proia, Stijn Matthys Elevated temperatures lead to a reduction of the bond strength of FRP (fibre reinforced polymer) reinforcement glued on concrete by ambient cured epoxy adhesive. This degrading behaviour is mainly observed for exposure temperatures beyond the glass transition temperature of the epoxy (Tg ≃ 60–80 °C) which is usually 2–3 times lower than the Tg of the matrix of pultruded FRP reinforcement. Contrary, lap shear tests on FRP-concrete systems made with carbon fibre reinforced polymer (CFRP) revealed an increase of the bond strength at temperatures close to the Tg of the epoxy adhesive. Several explanations have been expressed for this unexpected trend. The most accredited hypothesis describes the increase of bond strength as a consequence of the induced restraint thermal effect between the CFRP and the concrete substrate, because of the different thermal elongation of the materials. In this work, the influence of the restraint thermal effect is investigated further in terms of influence on the ultimate load recorded by lap shear tests at elevated temperature and to understand better the underlying mechanism. The obtained outcomes have revealed that the evaluation of the restrained thermal action has to consider the influence of the bond length of the joint and the thermal degradation of the adhesive.
       
  • Modeling and reliability of insert in composite pyramidal lattice truss
           core sandwich panels
    • Abstract: Publication date: 1 August 2019Source: Composite Structures, Volume 221Author(s): Ge Qi, Li Ma, Shu-Yang Wang Valid configuration of inserts is commonly used for assembly in sandwich structures. Inherently, various uncertainty results in variability in mechanical characteristics of inserts, and need to be addressed adequately. This study explores the reliability of inserts in composite pyramidal lattice truss core sandwich panels. Finite element method is utilized to analyze the sources and sensitivity of uncertainty in mechanical properties of constituent materials and geometry of sub-components. To quantify the reliability of the insert structure in the presence of uncertainty, machine learning technology is used to investigate the uncertainty propagation by a statistical description. Failure probability is observed and the insert structure shows outstanding stability under pull-out loading. The thickness of face-sheets and the properties of the bonding interface play large roles in stiffness and strength, respectively. Suitable process controls should be implemented to maintain the both critical parameters at a high and stable level.
       
  • Cyclic response of RC composite bridge columns with precast PP-ECC jackets
           in the region of plastic hinges
    • Abstract: Publication date: 1 August 2019Source: Composite Structures, Volume 221Author(s): Rui Zhang, Qingli Meng, Qingjun Shui, Wei He, Kexu Chen, Minfei Liang, Zhaoyang Sun ECC characterized by its tensile strain-hardening behavior, high compressive strain and damage tolerance capacity is an ideal material in the plastic hinges of RC bridge columns. The existing studies have investigated the seismic performance of RC bridge columns with total ECC plastic hinges and indicated that was enhanced significantly. However, because the cost of ECC is high and total ECC plastic hinge still needs quite amount, it is difficult to be used in the engineering applications. In this study, the precast PP-ECC jackets were proposed to fabricate the ECC/RC composite section in the region of plastic hinges in RC bridge columns. The design theory of PP-ECC jackets was proposed and a total of four scaled RC bridge columns were designed and fabricated. One specimen was RC column for reference, and another one was a RC column with total ECC plastic hinge. The rest of two columns used precast PP-ECC jackets with two different thicknesses. The unilateral cyclic loading tests were performed. It was found that the RC columns using PP-ECC jackets exhibited superior and comparable structural performance compared to normal RC column and RC column with total ECC plastic hinge, respectively.
       
  • Isogeometric analysis for size-dependent nonlinear thermal stability of
           porous FG microplates
    • Abstract: Publication date: 1 August 2019Source: Composite Structures, Volume 221Author(s): Cuong-Le Thanh, Loc V. Tran, Tinh Quoc Bui, Hoang X. Nguyen, M. Abdel-Wahab In this article, we present for the first time a research analysis for the size-dependent effects on thermal buckling and post-buckling behaviors of functionally graded material micro-plates with porosities (imperfect FGM) using isogeometric analysis. A seventh-order shear deformation plate theory associated with the modified couple stress theory (MCST) is particularly imposed to capture the size-dependent phenomenon within imperfect FGM micro-plates. The material properties of imperfect FGM micro-plates with three different distributions of porosities including even, uneven and logarithmic-uneven varying across the plate thickness are derived from the modified rule-of-mixture assumption. The nonlinear governing equation for size-dependent imperfect FGM micro-plate under uniform, linear and nonlinear temperature rise is derived using the Von-Kármán assumption and Hamilton’s principle. Through numerical example, the effect of temperature rise, boundary conditions, power index, porosity volume fraction, porosity distribution pattern and material length scale parameter on thermal buckling and post-buckling behaviors of FGP micro-plates are investigated.
       
  • Polymer composite Belleville springs for an automotive application
    • Abstract: Publication date: 1 August 2019Source: Composite Structures, Volume 221Author(s): J.H.D. Foard, D. Rollason, A.N. Thite, C. Bell This paper investigates mathematical modelling and manufacturing of polymer composite Belleville springs, and their potential application. The original expression for load carrying capacity developed for metal springs is refined by considering the variation of elastic modulus and Poisson’s ratio of laminates in polar coordinates. A novel series spring stacking arrangement is proposed to achieve complex stiffness variation by progressive action. The experimental results show consistent effect of number of plies on the spring rate and compare well with the theoretical predictions. Although handmade, the variations in load carrying capacity is very small (∼10%) confirming manufacturing viability. It is shown that a smooth, variable spring rate curve can be produced by reducing slip-stick frictional forces with the use of spacers within the spring stacks. In one application, the composite springs are shown to offer significant vehicle dynamic performance improvement through reduction of the tyre contact patch force variation and vehicle body acceleration.
       
  • Seismic performance of non-ductile RC frames strengthened with CFRP
    • Abstract: Publication date: 1 August 2019Source: Composite Structures, Volume 221Author(s): Weihong Chen, Weirong Shou, Zehui Qiao, Shuangshuang Cui To study the seismic performance of non-ductile reinforced concrete (RC) frames strengthened with carbon fiber-reinforced polymer (CFRP), two 1/2-scale, 2-bay, 2-story RC frames were prepared and tested under combined axial load and cyclic lateral load. One of the RC frames served as a control specimen (bare specimen) and the other was strengthened with CFRP sheets (strengthened specimen) at its joint regions. Based on the hysteretic curves, the envelop curves, and several important indexes (e.g., strength, stiffness, ductility, energy dissipation capacity) of the two specimens, the performance of the employed seismic strengthening technique in improving the seismic performance of RC frames was discussed in detail. The experimental results indicated that the externally bonded CFRP reinforcement had little influence on the lateral stiffness of the RC frame. While the lateral strength of the strengthened RC frame increased by about 20% compared to the control RC frame. Furthermore, it is worth noting that the energy dissipation capacity of the strengthened RC frame is as much as 3.01 times that of the control RC frame. The test results of the current study indicate that the employed strengthening method can substantially improve the seismic performance of the strengthened RC frames.
       
  • Analysis of thick porous beams by a quasi-3D theory and isogeometric
           analysis
    • Abstract: Publication date: 1 August 2019Source: Composite Structures, Volume 221Author(s): Weihua Fang, Tiantang Yu, Le Van Lich, Tinh Quoc Bui We analyze mechanical behavior of porous beams by an effective computational approach based on isogeometric analysis (IGA). The quasi-3D theory is employed to take into account not only both normal and shear deformations without any shear correction factor, but also the thickness stretching effect, while the use of NURBS basis functions within the IGA framework can directly meet the first-order derivative demand of the quasi-3D theory. To demonstrate the accuracy and performance of the quasi-3D theory-based isogeometric analysis, mechanical static bending and natural frequency of porous beams are investigated via the proposed method. In porous beams, porosities are assumed to vary along the thickness direction and to distribute in uniform, symmetric, and asymmetric configurations. The effects of porosity distribution, volume fraction of porosity, boundary condition, length-to-height ratio, etc., on deflections, stresses, and fundamental frequencies of porous beams are systematically analyzed. Numerical results indicate that the porosity distribution significantly alters the deflection and natural frequency of porous beams with large thickness and high volume fraction of pores. The present study, thus, provides an incisive approach for investigation on mechanical responses of porous structures and useful insights into the porosity design to achieve appropriately natural frequency and deflection responses.
       
  • Stress analysis and strength prediction of composite laminates with two
           interacting holes
    • Abstract: Publication date: 1 August 2019Source: Composite Structures, Volume 221Author(s): E. Özaslan, M.A. Güler, A. Yetgin, B. Acar In this study, stress analysis and strength prediction were performed for carbon/epoxy laminates with holes in specific orientations using experimental and numerical techniques. The interaction between the holes was studied with reference to their positions and load direction. The maximum laminate stress at the edge of the holes was identified for different hole orientations. The critical region was determined by considering the maximum stress location at the hole edges. Linear and non-linear behavior around the hole edge was investigated by strain gauge measurements for different hole orientations. Final failure load was predicted for specimens with specific hole orientations by using the point stress criteria (PSC) method. Furthermore, the extended PSC (EPSC) method was proposed to predict the failure load for the specimens with specific hole orientations. The EPSC method was verified by experimental study.
       
  • Effects of blades inside a nozzle on the fiber orientation and
           distribution in fiber-reinforced cement-based materials
    • Abstract: Publication date: 1 August 2019Source: Composite Structures, Volume 221Author(s): Jong-Han Lee, Jong Wan Hu, Joo-Won Kang This study developed a nozzle with blades inside called the B-nozzle to improve the fiber orientation and distribution in fiber-reinforced cement-based materials. Numerical simulations were conducted to determine the shape parameters of the B-nozzle while considering the physical interactions between the flow of the cementitious material, the boundaries of the nozzle, and the movement and rotation of the fiber. Based on the shape parameters of the B-nozzle designed from the numerical simulations, experiments were conducted for two sizes of B-nozzles with diameters of 80 and 100 mm to evaluate the influence of the blades on the fiber orientation and distribution. Pouring equipment was also fabricated to maintain the flow direction and initial pressure condition during the tests. The dimensions of the specimen are defined as 130 mm × 130 mm × 260 mm in consideration of the sizes of the fiber and nozzle. A specimen was cut into six pieces to measure the fiber orientation and distribution on the cutting surfaces using image acquisition and processing techniques. Compared to conventional circular nozzles, the B-nozzles increased the mean fiber orientation coefficients by approximately 31–39% and the fiber distribution coefficients by 3–23%.
       
  • Nonlinear dynamic analysis of a double curvature honeycomb sandwich shell
           with simply supported boundaries by the homotopy analysis method
    • Abstract: Publication date: 1 August 2019Source: Composite Structures, Volume 221Author(s): Yingjie Zhang, Yongqiang Li Dynamics of a double curvature honeycomb sandwich shell with simply supported boundaries are studied in this paper. The nonlinear governing equations of the double curvature honeycomb sandwich shell subjected to transverse excitations are derived by using Hamilton’s principle and Reddy’s third-order shear deformation theory. Based on the homotopy analysis method, the average equations of the primary resonance and harmonic resonance are obtained. The influence of structural parameters, the transverse exciting force amplitude and transverse damping to the double curvature honeycomb sandwich shell are discussed by using the analytic approximation method. The amplitude-frequency response curves demonstrate softening nonlinearity in primary resonance (no internal resonance), hardening nonlinearity in 3 order superharmonic resonance and no jump phenomenon in 1/3 subharmonic resonance. The variation of nonlinear strength, multivalued jump point and multivalued region are detailed and discussed.
       
  • Free vibration and static deflection analysis of functionally graded and
           porous micro/nanoshells with clamped and simply supported edges
    • Abstract: Publication date: 1 August 2019Source: Composite Structures, Volume 221Author(s): H. Salehipour, A. Shahsavar, O. Civalek The static deflection and free vibration problem of functionally graded porous (FGP) cylindrical micro/nanoshells are analyzed using the concept of the modified couple stress theory. The governing equations of first order shear deformation theory (FSDT) are employed and solved by generalized differential quadrature (GDQ) solution method. Using the power low for the FG properties, and incorporating pore content effect, a modified power function is considered for modelling FGP material properties. The transverse deflection under transverse loading and free vibration are numerically presented for a cylindrical micro/nanoshell with simply and clamped edges. The influences of porosity type, porosity volume fraction, material properties, size scale parameter, and type of the boundary conditions on the static bending and free vibration of FGP micro/nanoshells are investigated.
       
  • A multifunctional lattice sandwich structure with energy harvesting and
           nonlinear vibration control
    • Abstract: Publication date: Available online 13 April 2019Source: Composite StructuresAuthor(s): Ye-Wei Zhang, Chang Su, Zhi-Yu Ni, Jian Zang, Li-Qun Chen A new multifunctional lattice sandwich structure consisting of a lattice sandwich beam, a nonlinear energy sink (NES) and a giant magnetostrictive material (GMM) is proposed in this research. This structure exhibits excellent self-vibration suppression and aeroelastic energy harvesting performance. The dynamic equations of the whole structure are established using Hamilton principle and Newton’s second law, and the Runge-Kutta algorithm is used to obtain the amplitude response of the beam coupled with NES and without NES, which can indicate the vibration control effect of NES. Moreover, the energy harvest effect of the structure with GMM is also analyzed through numerical simulation. And a comparative analysis of relevant parameters such as NES mass, spring stiffness and damping coefficient is also implemented. The results show that this new multifunctional lattice sandwich structure can achieve the desired effect of vibration suppression and energy harvesting, and proper adjustment of parameters will improve the effect. This study provides a new idea for related research on vibration control and energy harvesting.
       
  • Experimental Characterization of Delamination in Off-Axis GFRP Laminates
           during Mode I Loading
    • Abstract: Publication date: Available online 6 April 2019Source: Composite StructuresAuthor(s): Esben Lindgaard, Brian Lau Verndal Bak This work experimentally investigates the influence of the off-axis angle between the lamina orientation and the crack growth direction in mode I delamination of GFRP laminates having R-curve behaviour due to large scale bridging. Initial and steady-state fracture toughness are characterized for different configurations of two laminate designs using moment loaded DCB specimens. In layup design 1, the layers adjacent to the initial delamination are parallel and the off-axis angle is varied. For layup design 2, only the off-axis angle of layers adjacent on one side of the initial delamination is varied. Microscopy, fractography, and comparisons of R-curves are used as tools to classify the cracking behaviour. All off-axis configurations tested experienced crack migration from the initial crack plane. In layup design 1, a significant difference in initial fracture toughness are found as opposed to layup design 2 in which an insignificant difference in initial fracture toughness and steady-state fracture toughness, respectively, are found. The off-axis configurations of layup design 2 are associated with crack migration and intraply crack propagation. The transition from interlaminar to intraply crack propagation correlates with the location of off-axis fibers not supported by the initial delamination indicating a free edge effect of the DCB specimen.
       
  • Bending strength predictions of cross-laminated timber plates subjected to
           concentrated loading using 3D finite-element-based limit analysis
           approaches
    • Abstract: Publication date: 15 July 2019Source: Composite Structures, Volume 220Author(s): Mingjing Li, Josef Füssl, Markus Lukacevic, Christopher M. Martin, Josef Eberhardsteiner Cross-laminated timber (CLT) is an innovative wood product with increasing utilisations. It is well known that the orthotropic and inhomogeneous strength properties of wooden boards have a strong influence on the load bearing capacity of CLT plates, especially when the complex wood fibre distribution due to randomly occurring knots is considered. Thus, high safety factors are used in current standards and a generally accepted numerical tool for the strength prediction of CLT plates is still not available. In this paper, we combine recent advances in 3D numerical limit analysis and a knot reconstruction algorithm, where not only the bending strength of CLT plates under concentrated loading is estimated using the numerical approach, but also the scatter of strength properties resulting from the material’s inhomogeneities is investigated using a stochastic approach. For the latter, data collected during the grading process of wooden boards are condensed into so-called strength profiles for single wooden boards. The limit analysis approach then allows a time-efficient simulation of a large number of randomly assembled CLT plates. The comparison of the resulting strength predictions to experiments shows good agreement with respect to both the mean load bearing capacity and the statistical scatter of strength.
       
  • A phase field approach to simulate intralaminar and translaminar fracture
           in long fiber composite materials
    • Abstract: Publication date: 15 July 2019Source: Composite Structures, Volume 220Author(s): A. Quintanas-Corominas, J. Reinoso, E. Casoni, A. Turon, J.A. Mayugo The development of predictive numerical methods, which accurately represent the progressive failure of long fiber composite materials, is nowadays required for the achievement of optimized mechanical responses in terms of load bearing capacities of modern composite structures. In this investigation, two characteristic failure mechanisms of long fiber composites, denominated as intralaminar and translaminar fracture, are simulated by means of a novel version of the phase field (PF) approach of fracture. This numerical strategy encompasses a sort of gradient-enhanced damage formulation rooted in the Griffith theory of fracture, which is herewith extended for its use in composite laminates applications. In order to assess its verification and validation, the predictions obtained using the present formulation are compared against experimental results and two well-established alternative computational methods, which correspond to an anisotropic local-based continuum damage model and a cohesive zone model. The comparisons demonstrate that the PF approach with the proposed formulation provides reliable and robust predictions under quasi-static loading, but with a higher versatility regarding the potential of triggering arbitrarily complex crack paths with intricate topology over alternative techniques.
       
  • Large amplitude free vibrations of long FGM cylindrical panels on
           nonlinear elastic foundation based on physical neutral surface
    • Abstract: Publication date: 15 July 2019Source: Composite Structures, Volume 220Author(s): Hadi Babaei, Yaser Kiani, M. Reza Eslami In the current investigation, the small and large amplitude free vibration characteristics of long cylindrical panels made of FGMs is investigated using the higher order shear deformation shell theory and Donnell kinematic assumptions. The interaction of the panel with a nonlinear hardening/softening foundation in also included into the formulation. The properties of the panel are assumed to be graded across the thickness of the panel and assumed to be temperature dependent. Using the neutral surface concept, the three coupled motion equations of the shell are established and solved for the case of long panels which are immovable simply supported on straight edges. The solution method is based on the two step perturbation technique which results in a closed form expression for the frequencies of the panel as a function of the mid-point deflection. Numerical studies are first validated for the case of long FGM plates. Afterwards novel numerical results are given to show the effect of geometrical parameters, power law index, foundation stiffnesses and temperature elevation. As shown, temperature elevation results in the reduction in natural frequencies and enhancement of the frequency ratio of the panel. Also temperature dependency reduces the natural frequencies and frequency ratios of the panel.
       
  • Analytical solutions for elastic SH-waves propagating through an isotropic
           inhomogeneous layer
    • Abstract: Publication date: 15 July 2019Source: Composite Structures, Volume 220Author(s): M. Bednarik, M. Cervenka, P. Lotton, L. Simon Plane time-harmonic elastic SH-wave propagation through an isotropic inhomogeneous layer surrounded by two homogeneous half-spaces is studied in this article. The material properties of the inhomogeneous layer are assumed to be non-uniform along the thickness direction according to a distribution law described by the triconfluent Heun functions or their polynomial forms that contain a number of optional parameters. The general analytical solution of the governing equation for elastic SH-waves in the layer is presented. Employing optional parameters, the material-property profiles can be varied to a relatively large extent without the need to seek new solutions of the governing equation for a chosen material-property profile. If the wave speed is constant in the inhomogeneous layer, the derived analytical solution is exact; otherwise the analytical solution is approximate. As a part of this article, the method enabling to find an approximate analytical solution of the governing equation for predetermined material functions is also presented. The applicability of the analytical solutions are tested and discussed based on the representative examples, and at the same time, the analytical results are compared with numerical ones to demonstrate their validity.
       
  • Numerical analysis on impact response of ultra-high strength concrete
           protected with composite materials against steel ogive-nosed projectile
           penetration
    • Abstract: Publication date: 15 July 2019Source: Composite Structures, Volume 220Author(s): Ruizhe Shao, Chengqing Wu, Yu Su, Zhongxian Liu, Jian Liu, Shenchun Xu In order to investigate the impact behaviours of ultra-high strength concrete (UHSC) target protected with high-toughness lightweight energy absorption composite materials against the projectile penetration thoroughly, a numerical study using LS-DYNA is conducted at impact velocities between 540 m/s and 810 m/s. The major compositions of FE models are the same as those of experimental specimens which include steel wire mesh reinforced concrete (SWMRC) plates, UHMWPE fibre laminates, aluminium foam sheets and the protected UHSC. Numerical results involving depth of penetration (DOP), impact crater (exfoliated) diameter of SWMRC plates, localized damage and ballistic deviation of the projectiles are obtained and then compared with experimental data, where the numerical results show reasonable agreement with the test results. Based on the validated FE models, the projectile penetration process and the energy evolution between the target and the projectile are studied. In addition, a parametric analysis is conducted to investigate the influence of the arrangement order for present composite materials on DOP and impact resistance of reinforced UHSC target, as well as the ballistic deviation and deformation of the projectile. Results of this study indicate that for the current UHSC target, firstly, the ballistic deviation and projectile deformation are two important factors affecting the impact resistance of the target; secondly, the fibre laminates play a major role in the projectile ballistic deviation and the impact kinetic energy of the projectile is mainly absorbed by the concrete matrix, multilayer steel wire meshes and different densities of foam sheets.
       
  • Free vibration analysis of rotating functionally graded CNT reinforced
           composite cylindrical shells with arbitrary boundary conditions
    • Abstract: Publication date: 15 July 2019Source: Composite Structures, Volume 220Author(s): Zhaoye Qin, Xuejia Pang, Babak Safaei, Fulei Chu In this paper, a general approach is provided for the free vibration analysis of rotating functionally graded carbon nanotube reinforced composite (FG-CNTRC) cylindrical shells with arbitrary boundary conditions. General formulations are derived based on the first-order shear deformation theory, the Donnell-type kinematic assumptions, and the artificial spring technique. Coriolis and centrifugal effects due to rotation are taken into account in the shell model. By employing Chebyshev polynomials as admissible functions, the Rayleigh-Ritz method is employed to derive the equations of motion for rotating FG-CNTRC cylindrical shells. The approach proposed is validated by comparing the present results with those reported in literature. The traveling wave motions of rotating FG-CNTRC shells are investigated. The effects of geometric parameters, volume fraction of carbon nanotubes, and boundary conditions on shell vibrations are also evaluated.
       
  • Isogeometric HSDT approach for dynamic stability analysis of general
           anisotropic composite plates
    • Abstract: Publication date: 15 July 2019Source: Composite Structures, Volume 220Author(s): Erfan Shafei, Shirko Faroughi, Timon Rabczuk Due to wide application of anisotropic composite plates in modern engineering structures and they were studied rare in literature, the main goal of this work is to study dynamic stability analysis of general anisotropic composite plates. To this end, here, we use the advantages of isogeometric analysis (IGA) to develop a higher-order shear deformation theory (HSDT) framework. In this work, force-frequency curves are obtained for general anisotropic composite plates using novel IGA-HSDT approach which have been previously presented using conventional finite element for specially orthotropic plates. Based on observation, the developed method is higher-order accurate, stable for wide spectral frequency range of anisotropic plates, and efficient in capturing the mode-converging phenomenon. IGA-HSDT model affirmed that the thick plates are more sensitive to frequency convergence prior to divergence with respect to thin ones. Furthermore, C3 NURBS capture the discrete spectrum accurately which is important for explicit dynamic applications of anisotropic plates. Specifically, anisotropic plates with clamped boundaries and low slenderness ratios have mode-converging phenomenon in dynamic stability curves prior to fundamental mode divergence which is not detected in previous works.
       
  • Influence of stochastic perturbations of composite laminate layups on the
           aeroelastic flutter of a cantilevered plate wing
    • Abstract: Publication date: 15 July 2019Source: Composite Structures, Volume 220Author(s): Christian Nitschke, Angela Vincenti, Jean-Camille Chassaing A numerical study of the effect of uncertainties in ply angles and thicknesses on the flutter speed of a cantilevered composite plate wing was conducted in this paper. Reduction of the number of uncertain parameters was possible thanks to the use of the polar method, which also enabled a systematic analysis of the influence of material symmetries. From the polar domain of orthotropic laminates, several stacking sequences were reconstructed in order to propagate parametric uncertainties. Typical fabrication uncertainties on ply thicknesses and angles were considered in order to quantify their influence on the probabilistic aeroelastic response. The reduction of the set of stochastic parameters by the polar method enabled the use of a polynomial-chaos approach which was combined with machine-learning techniques in order to deal with the correlation and with discontinuities in the response surface. Results reveal that possible manufacturing tolerances cause significant deviations in the critical flutter speed from the nominal value, especially when mode switches occur. As these deviations surpass classical dimensioning margins, uncertainty quantification approaches can provide added safety.
       
  • Nanoscale bending properties of bio-inspired Ni-graphene nanocomposites
    • Abstract: Publication date: 15 July 2019Source: Composite Structures, Volume 220Author(s): Raghuram R. Santhapuram, Scott E. Muller, Arun K. Nair At the nanoscale, bone consists of a hierarchical structure of mineral crystals (hard material) and collagen (soft material). Inspired by bone’s nanoscale structure and properties, we design a nanocomposite with flexible pristine/polycrystalline graphene embedded in a hard Ni matrix. We model Ni graphene nanocomposites, with different structural arrangements for graphene in the Ni matrix. We use molecular dynamics to investigate the deformation of Ni-graphene nanocomposites under 3-point bending. We find that nanocomposites can deform approximately 30% more than pure Ni. The flexibility of the nanocomposite is optimally enhanced with a distance between graphene sheets greater than or equal to 3.05 nm. Polycrystalline graphene nanocomposites show approximately 15–20% improvement in bending modulus compared to pristine graphene nanocomposites. The increase in bending modulus of polycrystalline graphene nanocomposite is because polycrystalline graphene has higher interfacial shear strength compared to pristine graphene. We also find that the structural arrangement of graphene sheets is more important than increases in their volume fraction in the Ni matrix. These results suggest that graphene sheets scattered in the Ni-matrix is preferable to other structural arrangements. The results from this simulation could help in tuning nanocomposite with desired mechanical properties for various engineering applications.
       
  • Multiscale computational homogenization of woven composites from
           microscale to mesoscale using data-driven self-consistent clustering
           analysis
    • Abstract: Publication date: 15 July 2019Source: Composite Structures, Volume 220Author(s): Xinxing Han, Chenghai Xu, Weihua Xie, Songhe Meng Compared with the traditional phenomenological method, the multiscale simulation has significant advantages. This paper presents a methodology and computational homogenization framework to predict the macroscale behavior of woven composites based on fiber and matrix in microscale. The major challenge conducting multiscale analysis is the huge computational cost. To improve the efficiency, one of the reduced order models, which is called the data-driven self-consistent clustering analysis (SCA), is introduced and the multiscale framework is proposed by integrating two SCA solvers from different scales. The macroscale performance of 4-H satin weave carbon/carbon composites is investigated using the proposed framework. In order to reconstruct a real microstructure representative volume element (RVE), both microscale and mesoscale architectures are observed using scanning electron microscopy (SEM) and optical microscopy, and statistical geometry features are obtained. In addition, the SCA method is also verified by comparing the results with the finite element method (FEM). The uniaxial tension process is simulated using the multiscale approach, and strain/stress fields in both mesoscale and microscale can be captured simultaneously. Moreover, the uniaxial tensile experiments are also carried out to validate this framework, which shows high efficiency and great accuracy.
       
  • Free vibration, buckling and bending analyses of multilayer functionally
           graded graphene nanoplatelets reinforced composite plates using the NURBS
           formulation
    • Abstract: Publication date: 15 July 2019Source: Composite Structures, Volume 220Author(s): Chien H. Thai, A.J.M. Ferreira, T.D. Tran, P. Phung-Van In this study, a NURBS formulation based on the four-variable refined plate theory (RPT) for free vibration, buckling and static bending analyses of multilayer functionally graded graphene platelets reinforced composite (FG GPLRC) plates, for the first time, is proposed. The distributions of graphene platelets (GPLs) in the polymer matrix either uniformly or non-uniformly including different patterns are considered. The Young’s modulus of the nanocomposites is predicted by the modified Halpin–Tsai model, while the Poisson’s ratio and density mass are implemented by the rule of mixtures. Governing equations are derived and the NURBS formulation is employed to obtain natural frequencies, critical buckling loads and deflections of multilayer FG GPLRC plates. Thanks to continuous higher-order derivatives of NURBS basis functions in isogeometric analysis (IGA), the present approximation is easy to satisfy the C1-continuty requirement of the RPT model. In addition, a rotation-free technique is applied to eliminate the bending and shear slopes in the case of clamped boundaries. Effects played by GPLs weight fraction, GPLs distribution patterns, number of layers, thickness-to-length ratio are investigated. Numerical results indicate that the inclusion of GPLs can significantly improve the stiffness of plates.
       
  • Fabrication, properties and failure of 3D stitched carbon/epoxy composites
           with no stitching fibers damage
    • Abstract: Publication date: 15 July 2019Source: Composite Structures, Volume 220Author(s): Jia-qian Xuan, Dian-sen Li, Lei Jiang Three-dimensional (3D) stitched carbon/epoxy composites with no stitching fibers damage were fabricated successfully. The fracture toughness, high-temperature flexural response and failure mechanism of 3D stitched composites are reported. The results show fabricated 3D stitched composites with no stitching fibers damage have excellent Model II interlaminar fracture toughness and flexural properties. The temperature is an important parameter affecting the properties of composites and the measured flexural performance decreases with increasing the temperature. The composite exhibits brittle fracture feature, and the destruction is originates from matrix cracking, and a gradual process from compression and tension surface to the interior layers, while the stitching fibers can effectively prevent and change the cracks’ propagation paths. Fiber/matrix interface debonding caused by elevated temperature is the main mechanism for material failure.
       
  • Strengthening of reinforced concrete structure using sprayable
           fiber-reinforced cementitious composites with high ductility
    • Abstract: Publication date: Available online 13 April 2019Source: Composite StructuresAuthor(s): Bo-Tao Huang, Qing-Hua Li, Shi-Lang Xu, Bin Zhou Fiber-reinforced cementitious composites with high ductility exhibit significant pseudo-strain-hardening response and multi-cracking behavior. In this paper, a systematical investigation of a sprayable fiber-reinforced cementitious material with high ductility is presented from material design to practical application. This sprayable material is formed using the wet-mix spray process, and its compressive, tensile, and flexural strengths are higher than those of the cast ones with the same proportion. A series of reinforced concrete beams, including unloaded and pre-loaded ones, is strengthened with this material, and the four-point bending test is performed to evaluate the flexural performance of the composite elements. Theoretical analysis is conducted to predict the load capacity of the specimens. The application cases of this sprayable material in China are presented to show its potential application in the construction of durable concrete structures and restoration of aged structures.
       
  • Shakedown of porous material with Drucker-Prager dilatant matrix under
           general cyclic loadings
    • Abstract: Publication date: 15 July 2019Source: Composite Structures, Volume 220Author(s): J. Zhang, A. Oueslati, W.Q. Shen, G. De Saxcé This paper is concerned with the shakedown limit states of porous ductile materials with Drucker-Prager matrix under cyclically repeated loads. Using the hollow sphere model and Melan’s shakedown theorem based on time-independent residual stress fields, a macroscopic fatigue criterion is derived for the general conditions of cyclic loads. First, the case of the hollow sphere subjected to pure hydrostatic loading is studied and the limit states of collapse by fatigue or by development of mechanism are derived. Then, the general case involving shear effects with any arbitrary cyclic load fluctuations ranging from the pulsating load to the alternating one is considered. The key idea is in two steps: (i) the choice of appropriate trial stress and trial residual stress fields and (ii) then maximizing the size of the load domain in the spirit of the standard lower shakedown theorem. The new macroscopic shakedown criterion depends on the porosity, the friction angle, Poisson’s ratio, the two stress invariants of the effective stress tensor and the sign of the third one. Together with the limit analysis-based yield criterion corresponding to the sudden collapse by development of a mechanism at the first cycle, it defines the safety domain of porous materials subjected to cyclic load processes. Interestingly, it is found that the safe domain is little sensitive to variations of the friction angle, however, it is considerably reduced compared to the one under monotonic loads obtained by limit analysis. Finally, a comparative study between the analytical results and numerical predictions performed by micromechanics-based finite element simulations is conducted for different porosities and friction angles.
       
  • Investigation on Low Velocity Impact Behavior of Sandwich Composite and
           Monolithic Laminate Plates using FEM Analysis
    • Abstract: Publication date: Available online 9 April 2019Source: Composite StructuresAuthor(s): Hyunbum Park Because the fiber composite approach can provide significant improvement in specific strength and stiffness over conventional metal alloys, the consuming demand is getting more increase. Moreover, the composite material structures are more effective in economic point of view due to great reduction of number of parts and manufacturing processes relatively to the conventional metal structure. However the composite structures has an disadvantage for instance, very weak for impact damage due to foreign object damage such as, sand, rock, birds, tool, etc. Especially the damage due to low velocity impact rather than that by high velocity impact cannot be visually found. Such the low velocity damage can be divided into some types such as matrix cracking, fiber fracture, delamination, etc. In this study low velocity impact behaviors of monolithic laminate plate were investigated and sandwich composite plate compared using a commercial FEM Code.
       
  • Dynamic performances of basalt fibre laminates at room and low
           temperatures
    • Abstract: Publication date: Available online 9 April 2019Source: Composite StructuresAuthor(s): I. Papa, A. Langella, V. Lopresto Basalt fibre reinforced plastic laminates in vinyl ester resin were obtained by overlapping plain woven fabrics by resin infusion technique. Rectangular specimens, 100mm x 150mm, were cut from the original panels and impacted at penetration and increasing energy values, at two different temperatures (room and -50°C). The final aim was to investigate the damage onset and propagation to study the dynamic behaviour in extreme conditions of basalt laminates, correlating the absorbed energy to the impact one and to evaluate the possibility to replace the traditional carbon and glass laminates in fields where the temperature plays an important role.
       
  • Micromechanical analysis of interlaminar crack propagation between angled
           plies in mode I tests
    • Abstract: Publication date: Available online 9 April 2019Source: Composite StructuresAuthor(s): L.F. Varandas, A. Arteiro, G. Catalanotti, B.G. Falzon This paper presents a micromechanical finite element model to study interlaminar damage propagation and relocation, known as delamination migration, between angled plies, consisting of a double-ply θ/0° Unit Cell (UC) in-between homogenised unidirectional 0∘ plies. Random fibre distributions and appropriate constitutive models are used to model the different dissipative phenomena that occur at crack onset and propagation. Varying the upper ply fibres orientation, θ, and ply thickness, it is possible to assess their influence on the damage migration mechanism. Different features associated with delamination migration are analysed, such as the distribution of interlaminar shear stresses at the crack tip and the kink angles. When comparing the results of the micromechanical model with previously conducted experimental observations, similar trends are obtained. It is concluded that the computational framework is able to simulate mode I interlaminar damage propagation and delamination migration in multidirectional laminates, providing a sound tool to better understand the conditions behind interlaminar crack migration.
       
  • Robotic filament winding: an innovative technology to manufacture complex
           shape structural parts
    • Abstract: Publication date: Available online 9 April 2019Source: Composite StructuresAuthor(s): Luca Sorrentino, Emmanouel Anamateros, Costanzo Bellini, Luigi Carrino, Giuseppe Corcione, Antonio Leone, Gianluca Paris The robotic filament winding (RFW) technology consists of an industrial robot that is equipped with a feed and deposition systems; they are suitable for placing a tape along the stress directions the part is subjected to during operation. RFW cell replaces the human operator that is the only system that has been previously used to manufacture complex shape parts. It represents an advantage as regards process control, repeatability and manufacturing times. The present work focuses on the family of structural parts whose shape may be obtained as a result of a full section sweeping along a closed non auto-intersecting 3D curve. The aim of the paper is to present a design methodology for the forming process of complex shape structural parts by RFW, in order to obtain structural homogeneity and fibre content uniformity, and so to demonstrate the potential of an innovative robotic cell for manufacturing these parts.
       
  • Dynamic buckling analyses of functionally graded carbon nanotubes
           reinforced composite (FG-CNTRC) cylindrical shell under axial power-law
           time-varying displacement load
    • Abstract: Publication date: Available online 9 April 2019Source: Composite StructuresAuthor(s): Peng Jiao, Zhiping Chen, You Li, He Ma, Jihang Wu In this paper, a semi-analytical approach is proposed to investigate the dynamic buckling behavior of functionally graded carbon nanotubes reinforced composite (FG-CNTRC) cylindrical shell under dynamic displacement load. Five types of carbon nanotubes (CNTs) distribution are considered, in which the uncertainty of CNTs distribution is also taken into account. Combining with the first-order shear deformation theory and von-Kármán strains, the nonlinear governing equations for dynamic buckling analysis of FG-CNTRC cylindrical shell considering the thermal effects are derived. Then, Galerkin method and the fourth-order Runge-Kutta method are employed to solve the governing equations. And the dynamic critical buckling condition of FG-CNTRC cylindrical shell is determined by the Budiansky-Roth criterion. Compared with the published literatures, the feasibility and accuracy of proposed analysis approach are validated. Finally, the parametric studies are systematically carried out to analyze the effects of CNTs distribution type, CNTs volume fractions, the uncertainty of CNTs distribution, the loading rate and form of dynamic displacement load, structural characteristics and temperature on the dynamic buckling behavior of FG-CNTRC cylindrical shell.
       
  • Mechanical performance evaluation of sandwich panels exposed to slamming
           impacts: Comparison between experimental and SPH results
    • Abstract: Publication date: Available online 9 April 2019Source: Composite StructuresAuthor(s): O.H. Hassoon, M. Tarfaoui, A. El Moumen, Y. Qureshi, H. Benyahia, M. Nachtane Slamming is a dynamic phenomenon in which a high magnitude pulse peak pressure occurs in a short time duration when the bottom structure of a ship impacted against the sea surface. This phenomenon can cause damage in the structure due to fluid-structure interaction (FSI) thus, plays a vital role in designing and manufacturing of ships for naval applications. In this paper, high performance sandwich structure, having many opportunities and challenges for the marine structural design, were studied experimentally using a high-speed shock test machine to examine the water entry problem. In addition, a velocity control system was used to calibrate and preserve the approximately uniform velocity throughout the slamming impact. Sandwich panels with different thicknesses i.e. 27mm and 37mm therefore, having different stiffness’s were exposed under constant impact velocities of 6 and 8 m/s at the deadrise angle 10°. Experimental results were then compared and verified by the numerical investigation based on explicit Smoothed Particle Hydrodynamics (SPH) method. This study focuses on the overall structural response, deformation, and hydrodynamic response of the structure during the dynamic impact designed for naval applications.
       
  • Effect of heterogeneous interphase on the mechanical properties of
           unidirectional fiber composites studied by FFT-based method
    • Abstract: Publication date: Available online 9 April 2019Source: Composite StructuresAuthor(s): Bing Wang, Guodong Fang, Shuo Liu, Jun Liang Based on representative volume element (RVE) with interphase region between fiber and matrix, the microscopic mechanical behavior of transversely randomly distributed unidirectional (UD) carbon fiber reinforced polymer composites is studied by using fast Fourier transforms (FFT) simulation. The change of mechanical properties across interphase region can be described by an exponential function. By using FFT method, the effect of fiber volume fraction and interphase properties distribution on the effective material properties and the damage development mechanism of the composites are investigated. The effect of heterogeneous behaviors of carbon fiber with core/shell like behavior and interphase is also discussed. Compared to the traditional finite element model with zero-thickness interface, the stress-strain results obtained by the present computational approach are in good agreement with experimental data. This study can be helpful for interface design and manufacturing of fiber reinforced composites.
       
  • Effect of the cutting speed on the cutting mechanism in machining CFRP
    • Abstract: Publication date: Available online 8 April 2019Source: Composite StructuresAuthor(s): Youliang Su Cutting mechanism of CFRP is different from that of a homogeneous metal. For metal, high speed cutting can improve machining quality and efficiency. However, there is no agreed conclusion on the effect of cutting speed on the cutting mechanism of CFRP. This paper studies the effect of cutting speed on cutting mechanism of CFRP and damage formation by using finite element and experiment methods. A three-dimensional finite element model of orthogonal cutting CFRP is established considering the strain-rate-dependent mechanical properties of resin and the anisotropy of fiber. By this model, cutting processes at micro level are simulated. Fracture evolution processes of fiber and resin are characterized. Furthermore, experimental data of cutting forces are obtained, and the machined surface microstructure are observed based on orthogonal cutting experiments. Subsurface morphology and degree of resin cracking extension in simulation and experiment are consistent with each other. Results show that with the increase of cutting speed, the fiber deformation and the affected area before fiber fracture obviously deceases. Accordingly, the resin cracking and extension degree caused by the excessive deformation of fiber also be greatly reduced. In addition, there is a trend that the specific energy gap for different chip formation modes becomes smaller and smaller.
       
  • A second-order multiscale approach for viscoelastic analysis of
           statistically inhomogeneous materials
    • Abstract: Publication date: Available online 6 April 2019Source: Composite StructuresAuthor(s): Zhiqiang Yang, Yi Sun, Yizhi Liu, Qiang Ma An effective second-order multiscale approach is developed in this work to discuss viscoelastic properties of statistically inhomogeneous materials. In these materials, the sophisticated microscale structure of inclusions, including related shape, orientation, size, spatial distribution, volume fraction and so on, results in varying of the macroscale properties. At first, the Laplace transform is applied to the linear viscoelastic problems, and expected relaxation modulus in Laplace domain for the materials is given. Also, the second-order multiscale formulas for evaluating the viscoelastic problems of statistically inhomogeneous materials are derived. Next, the stochastic multiscale algorithm is proposed, and the expected relaxation moduli in time domain are obtained by the least-square and inverse Laplace transform. The salient features of the proposed approach are the asymptotic high-order homogenizations that do not require high-order continuity of the coarse-scale (or macroscale) solutions and can handle the random materials with complicated microstructure at a fraction of computational cost. Finally, some examples for the composites are computed by the effective algorithm, and compared with the data by the theoretical models and experimental results. The comparison illustrates that the stochastic multiscale model is efficient for determining the viscoelastic properties of the materials and shows their potential application in practical engineering calculation.
       
  • Tria and Quad plate finite elements based on RZT(m) for the analysis of
           multilayered sandwich structures
    • Abstract: Publication date: Available online 6 April 2019Source: Composite StructuresAuthor(s): Marco Gherlone Aim of the paper is to develop and to assess a class of plate finite elements for the analysis of multilayered composite and sandwich structures. The adopted model is the mixed Refined Zigzag Theory (RZT(m)), based on the kinematics of the Refined Zigzag Theory (RZT) and on the assumption of transverse shear stresses coming from integration of indefinite equilibrium equations. A triangular and quadrilateral flat finite element are developed by means of the Reissner’s Mixed Variational Theorem and an interpolation strategy to eliminate shear locking. Several numerical examples are discussed to demonstrate the accuracy of RZT(m) and related finite elements for static response, free-vibrations and critical load problems of sandwich structures.
       
  • High-cycle fatigue constitutive model and a load-advance strategy for the
           analysis of unidirectional fiber reinforced composites subjected to
           longitudinal loads
    • Abstract: Publication date: Available online 6 April 2019Source: Composite StructuresAuthor(s): Lucia G. Barbu, Sergio Oller, Xavier Martinez, Alex H. Barbat A fatigue constitutive model valid for the composite constituent will be presented in this paper. The composite behaviour will be obtained by means of the serial/parallel mixing theory that is also used as a constitutive equation manager. The constitutive formulation is coupled with a load advancing strategy in order to reduce the computational cost of the numerical simulations. Validation of the constitutive formulation is done on pultruded glass fiber reinforced polymer profiles. Special emphasis is made on the comparison between the experimental and the numerical failure mode.
       
  • Functionally graded zirconium oxide coatings produced on zirconium using
           induction heat treatment
    • Abstract: Publication date: 15 July 2019Source: Composite Structures, Volume 220Author(s): Aleksandr Fomin Zirconium oxide coatings were produced by induction heat treatment (IHT) of E110 zirconium. The IHT was performed at temperatures within 600–1200 °C for 30–300 s. According to the results of scanning electron microscopy (SEM), energy dispersive analysis (EDX), X-ray diffraction (XRD), and nanoindentation, zirconium oxide coatings with high hardness of 44.56 ± 7.40 GPa (at load of 10 mN), 25.76 ± 2.78 GPa (at load of 200 mN), and elastic modulus of 387 ± 55 GPa (at load of 10 mN), 372 ± 20 GPa (at load of 200 mN) were formed on zirconium by IHT at 800–850 °C for 300 s. The functionally graded oxide coatings consisted of a mixture of α-ZrO2 (baddeleyite) and γ-ZrO2 (cubic zirconia), the oxygen concentration on the surface reached a maximum of 69.52 ± 3.16 at% and the thickness of the oxygen-rich layer was about 8–10 μm.
       
  • Low-velocity impact responses and CAI properties of synthetic foam
           sandwiches
    • Abstract: Publication date: Available online 6 April 2019Source: Composite StructuresAuthor(s): Jun Wang, Jing Li, Hota GangaRao, Ruifeng Liang, Jiye Chen This paper presents experimental and analytical studies on impact and compression after impact (CAI) responses of sandwiches with glass fiber reinforced polymer (GFRP) skins and synthetic foam cores under low-velocity impacting. The impact test results showed that the penetration depth of GFRP panels with synthetic foam is much smaller than that of bare synthetic foam panels. The edgewise compression test results indicated the facesheet debonding dominates the failure mode of the sandwich panels without lattice webs, while the failure mode of the sandwich panels with lattice webs is predominated by the wrinkling and delamination of the facesheets and the crushing of foam core. The influences of applied impact energy, GFRP lay-up, synthetic foam density and the existence of webs on the impact and post impact behavior of sandwich panels are discussed herein. Analytical models are proposed to predict the residual ultimate edgewise compressive load capacity of sandwich panels with lattice webs after impacts, using energy principles and variational methods in applied mechanics. The influences from impact damage, the local buckling of the facesheets and the confined strength of the foam core are measured and compared well with proposed analytical models.
       
  • Improvement of tufting mechanism during the advanced 3-Dimensional tufted
           composites manufacturing: To the optimisation of tufting threads
           degradation
    • Abstract: Publication date: Available online 6 April 2019Source: Composite StructuresAuthor(s): Chan Hui, Peng Wang, Xavier Legrand Tufting is an ongoing technique to manufacture the 3-dimensional (3D) textile reinforcement for composites. The inserted tufting threads provide a good mechanical performance through-the-thickness of the final composite parts. However, the degradation of inserted tufting thread can be experienced during the tufting process. This degradation brings out the negative influence on the mechanical performance of the reinforced tufting thread and of the composite, which is not yet studied and analysed. In the present work, to improve the understanding of tufting threads degradation, the image-observation analysis and the mechanical testing are firstly carried out to the inserted threads taken from the conventional tufting process. In addition, the effect of tufting density on the threads degradation is investigated. An improved tufting mechanism by adding a guide needle without tufting threads is proposed to reduce the inserted threads degradation. The results show that in the improved tufting process the threads degradation decreases 30% compared to the conventional tufting and the tensile performance of the inserted threads has a significant improvement.
       
  • Improved tensile strength of carbon nanotube-grafted carbon fiber
           reinforced composites
    • Abstract: Publication date: Available online 6 April 2019Source: Composite StructuresAuthor(s): Geunsung Lee, Minchang Sung, Ji Ho Youk, Jinyong Lee, Woong-Ryeol Yu Increased tensile strength of carbon nanotube (CNT)-grafted carbon fiber (CF) composites has been reported, but the mechanism of this increase is not yet clear. In this study, CNT-grafted CF unidirectional (UD) and woven composites were fabricated using a low- temperature chemical vapor deposition (CVD) and resin transfer molding. Two types of CNTs (short and thin, long and thick) were successfully grown and grafted to CFs without degrading the CFs in the preforms. The CNT-grafted CFs exhibited increased interfacial shear strength (IFSS) similarly regardless of the CNT type. Interestingly, however, long and thick CNT-grafted CF UD and woven composites exhibited significant increases in tensile strength (about 20% and 30%), suggesting other mechanisms besides increased IFSS. The splitting crack initiation under the mixed mode condition was quantitatively characterized for the CNT-grafted CF UD composites, demonstrating that long and thick CNTs delayed the splitting crack initiation. Delayed fiber splitting and increased IFSS were concluded to be the main sources of increased tensile strength of CNT-grafted CF composites.
       
  • A three-dimensional fracture pattern diagram of staggered platelet
           structures
    • Abstract: Publication date: Available online 6 April 2019Source: Composite StructuresAuthor(s): Youngsoo Kim, Heeyeong Jeong, Grace X. Gu, Seunghwa Ryu In order to design composites that mimic the remarkable balance of properties such as strength, toughness, and stiffness of staggered platelet structures in nature, it is crucial to understand their load transfer and failure mechanisms. Recently, we proposed an analytical model to predict the stress distribution within staggered platelet structures for a wide range of constituent materials’ moduli and geometric parameters in the elastic response regime. Here, based on the model, we construct the fracture pattern diagram featuring three distinct mechanisms categorized according to the failure sequences of soft tip, soft shear zone, and hard platelet. The proposed fracture map is capable of capturing the transition of failure mechanisms observed in crack phase field simulations and draws parallels to mechanisms seen in experiments. Our study sheds light on the origin of failure mechanism transitions and enables rational designs of future staggered platelet composites with unprecedented properties.
       
  • The effect of chemical changes during thermal modification of European oak
           and Norway spruce on elasticity properties
    • Abstract: Publication date: Available online 6 April 2019Source: Composite StructuresAuthor(s): Milan Gaff, František Kačík, Dick Sandberg, Marián Babiak, Marek Turčani, Peter Niemz, Peter Hanzlík The elasticity in bending of European oak (Quercus robur L.) and Norway spruce (Picea abies (L.) Karst.) timber was evaluated before and after thermal modification and related to the changes in chemical composition of the wood as a result of the modification. A new software was developed (MATESS) and used to identify characteristic points on the force-deformation diagram. The modulus of elasticity (MOE), stress at the limit of proportionality (LOP) and elastic potential (PE) were used to describe the wood properties. Extractives, lignin, cellulose, holocellulose, and hemicelluloses were analysed to reveal the patterns that occur during the loading of the specimens. Thermal modification lowers the mechanical properties (MOE, LOP and PE) of oak and spruce wood, and the reduction increases with increasing modification temperature. Changes in chemical composition of thermally modified wood show a strong relationship to the reduction in elasticity properties for bot species.
       
  • Prediction of the mechanical behavior of fiber-reinforced composite
           structure considering its shear angle distribution generated during
           thermo-compression molding process
    • Abstract: Publication date: Available online 6 April 2019Source: Composite StructuresAuthor(s): Dug-Joong Kim, Myeong-Hyeon Yu, Jaeyoung Lim, Byeunggun Nam, Hak-Sung Kim In this study, a combined forming-structural analysis of composite structures was performed. Fiber orientation and shear angle changes of the composite materials during its thermo-compression molding processes were predicted with commercial software PAM-FORM. In addition, the material properties, such as elastic modulus and strength, from the shearing of woven fabrics, were measured. The predicted shear angle changes were transformed and reflected to the structural analysis by a self-developed vector-mapping program. The load-displacement curves of the composite structures from the combined forming and structural simulation were compared with the experimental compression and bending test results of hemispherical and U-shaped components, respectively. Finally, it was found that the mechanical behaviors of composite structures can be accurately predicted by the developed combined thermo-forming structural analysis method.
       
  • Soft Body Armor Time-Dependent Back Face Deformation (BFD) with Ballistics
           Gel Backing
    • Abstract: Publication date: Available online 6 April 2019Source: Composite StructuresAuthor(s): T. Goode, G. Shoemaker, S. Schultz, K. Peters, M. Pankow This paper presents a method for obtaining time dependent back face deformation (BFD) data for body armor during ballistic impact using a clear ballistics gelatin backing and high-speed cameras to capture the deformation profile. Using this method, baseline fabric characterization data was obtained for samples comprised of varying layers of 467 g/m2 Kevlar K29 fabric impacted with 8.24 g steel ball projectile and backed with NATO standard 20% clear ballistics gelatin. For these tests, deformation depths were seen to increase with increasing impact energy and decreasing total areal density. A limited study of the various test parameters was performed by testing one additional fabric, projectile, and ballistics gelatin. From these comparisons, it was observed that 122 g/m2 Kevlar KM2+ fabric performs better per weight than 467 g/m2 Kevlar K29 fabric in terms of BFD, 9 mm FMJ projectiles produce deeper BFDs than 12.7 mm steel ball projectiles, and backing a sample with FBI standard 10% ballistics gel increases the BFD considerably over NATO standard 20% ballistics gel.
       
  • A unified Jacobi-Ritz formulation for vibration analysis of the stepped
           coupled structures of doubly-curved shell
    • Abstract: Publication date: Available online 6 April 2019Source: Composite StructuresAuthor(s): Bin Qin, Kwanghun Kim, Zhonggang Wang, Qingshan Wang The free vibration of different kinds of stepped coupled doubly-curved shell structures with elastically constrained edges are investigated by adopting the Jacobi-Ritz method for the first time. Coupled structures are comprised of substructures, where paraboloidal, hyperbolical, elliptical, and cylindrical stepped shells are typical ones. The Flügge’s thin shell theory is utilized to construct the analytical model, together with the multi-segment partitioning strategy. For each shell segment, despite of various boundary conditions, the displacement components along the meridional directions are expressed by Jacobi polymials and those along the circumferential directions are represented by Fourier series. Then the unknown coefficients of the displacements are obtained by introducing the Rayleigh-Ritz method. The solutions proposed here for coupled structures have two main advantages: first, there is no need to vary the displacement or the motion equations; and secondly, the efficiency of modeling can be notably enhanced. By comparison with (Finite Element method) FEM and others’ results, the reliability of current method can be validated. At last, the free vibrations of different kinds of coupled structures containing stepped shell are analyzed by presenting several numerical examples, the results of which may be served as reference data.
       
  • Behaviour of CFRP Strengthened CHS Members under Monotonic and Cyclic
           Loading
    • Abstract: Publication date: Available online 6 April 2019Source: Composite StructuresAuthor(s): Tafsirojjaman, Sabrina Fawzia, David Thambiratnam, Xiao-Ling Zhao Tubular hollow members, though used in many civil and mechanical applications, are highly vulnerable structural elements when subjected to cyclic loading. They have been used extensively in both onshore and offshore civil infrastructure where cyclic loading can result from earthquake, waves, currents and wind. Due to service loads increment, errors in design, effect of severe environments or loss of material properties, tubular hollow steel members may require to undergo strengthening to withstand both static and cyclic loads. In the present study, a series of experiments on bare and externally-bonded carbon fibre reinforced polymer (CFRP) strengthened CHS steel members subjected to monotonic and cyclic loading has been conducted to investigate the effect of CFRP strengthening technique on the structural behaviour of strengthened members. The results showed that the CFRP strengthening is effective to enhance the cyclic performance of CHS steel members by improving the moment capacity, moment degradation behaviour, secant stiffness, energy dissipation capacity and ductility compared to bare steel CHS members. In addition, the moment capacity of CHS members has been improved under monotonic loading due to the CFRP strengthening as well. Moreover, the impact of adhesive types on the structural response of the strengthened specimens was also investigated.
       
  • Density gradient tailoring of aluminum foam-filled tube
    • Abstract: Publication date: Available online 6 April 2019Source: Composite StructuresAuthor(s): Zhang Yi, He Si-yuan, Liu Jia-gui, Zhao Wei, Gong Xiao-lu, Yu Jin Metallic foam with uniform pore structure has been used as a filling material for the thin-walled tube to improve the structural crashworthiness. Homologous natural porous materials, such as bone, adopt graded pore structures and exhibit excellent performance. Inspired by the biological mechanism of adaptive remodeling in bone, this study proposes a density tailoring method on the foam filler to further improve the energy absorption of the composite structure. This method designs the density gradient of foam filler depending on the internal plastic strain distribution calculated by Finite Element (FE) analysis. The requisite material parameters of aluminum foam for the FE model, including the hardening curves and the plastic Poisson’s ratios, are obtained through experiments. The simulation results demonstrate that the outer part of foam filler exhibits a higher strain level than the inner part when adhesive effect is applied at the foam/tube interface. Radial density gradients are developed for the foam fillers to align with the FEA strain distribution pattern. The graded foam-filled tubes exhibit up to 24% higher specific energy absorptions (SEA) than the equal-weight uniform foam-filled tubes in FE simulations.
       
  • A Novel Method for Testing and Determining ILSS for Marine and Offshore
           Composites
    • Abstract: Publication date: Available online 6 April 2019Source: Composite StructuresAuthor(s): Abedin I. Gagani, Andrey E. Krauklis, Erik Sæter, Nils Petter Vedvik, Andreas T. Echtermeyer A novel method is proposed for interlaminar shear testing of marine composites, which accelerates fluid saturation: the I-beam short beam shear test. A layered finite element (FE) model is employed to explain the nonlinear behavior of the short beam shear experiment. Using this model, rectangular and I-beam short beam shear results are compared, yielding consistent results. Dry and saturated specimens are also compared for the I-beam geometry proposed. The model can simulate these effects and enables attributing the nonlinear behavior of the composite interlaminar shear response to the plasticity of the resin rich inter-ply. In both dry and saturated conditions, the interlaminar shear strength of the composite can be estimated mainly from the matrix properties.
       
  • Concurrent topology design of structures and materials with optimal
           material orientation
    • Abstract: Publication date: Available online 6 April 2019Source: Composite StructuresAuthor(s): Xiaolei Yan, Qiwang Xu, Dengfeng Huang, Yong Zhong, Xiaodong Huang A concurrent optimization design method for the topologies of structures and materials and the material orientation is presented based on bi-direction evolutionary structural optimization (BESO) method. The macrostructure is assumed to be composed of a uniform cellular material but with different orientation. The homogenization technique is used to calculate the effective properties of the cellular material which builds a connection between material and structure. An analytical method, which is flexible to deal with the shear “weak” and “strong” materials, is proposed to solve the material orientation optimization problem. The optimization algorithm considering the simultaneous optimization of topologies of macrostructures and material microstructures, and material orientations is developed. Numerical examples are presented to demonstrate the effectiveness of the proposed optimization algorithm and show that concurrent topology design of structures and materials with material orientation optimization can greatly improve the structural performance.
       
  • Evaluation of cracking patterns of cement paste containing polypropylene
           fibers
    • Abstract: Publication date: Available online 6 April 2019Source: Composite StructuresAuthor(s): SZELĄG Maciej The article analyzes cracking patterns on the surface of a cement matrix modified with polypropylene fibers. Cracks analyzed were caused by the effect of an elevated temperature. In order to quantify cracking patterns, image analysis tools were used to define three stereological parameters. In total, 4 series of samples were tested, two of them were modified with polypropylene fibers. In each individual series the samples were made with a variable w/c ratio, which was equal to 0.4, 0.5, and 0.6 respectively. A microstructure analysis was also carried out using a scanning electron microscope and an X-ray microanalyser. The results obtained allowed to determine the impact of polypropylene fibers on the geometry of thermal cracks of pastes, which was largely dependent on the class of the cement used. The elements of the theory of dispersion systems were used to explain the ongoing relationship.
       
  • Vibration and acoustic properties of composites with embedded lithium-ion
           polymer batteries
    • Abstract: Publication date: Available online 5 April 2019Source: Composite StructuresAuthor(s): Joel Galos, Akbar Afaghi Khatibi, Adrian P. Mouritz Composite structures containing lithium-ion polymer (LiPo) batteries are being developed for energy storage on motor vehicles and other applications. This paper presents an experimental and numerical study into the effect of embedding (LiPo) batteries into carbon fibre laminates and sandwich panels on the vibration and acoustic properties. The vibration responses (modal frequencies, damping) were measured experimentally using Laser Doppler vibrometry and calculated numerically using finite element modal analysis. The results reveal that careful placement of LiPo batteries within composite structures is needed to control the vibration properties. Embedding batteries at the nodal points increases the vibration bending damping ratio for modes II and III, with improvements of up to 220% (mode II) and 310% (mode III) for the laminate and sandwich composite, respectively. LiPo batteries also improve the acoustic performance by increasing the coincidence frequency and decreasing the wavenumber amplitude at frequencies above the first vibration bending mode. The results indicate that the judicious placement of embedded LiPo batteries can improve the vibration damping properties of both carbon fibre laminates and sandwich composites.
       
  • Low velocity impact response of fibre metal laminates based on aramid
           fibre reinforced polypropylene
    • Abstract: Publication date: Available online 5 April 2019Source: Composite StructuresAuthor(s): J.G. Carrillo, N.G. Gonzalez-Canche, E.A. Flores-Johnson, P. Cortes In this work, the low velocity impact behaviour of thermoplastic fibre metal laminates (FMLs) made of aramid fibre reinforced polypropylene and aluminium alloy Al 5052-H32 is presented. The impact behaviour of these FMLs and their constituent materials was determined using a drop-weight impact tower. Force-time curves were used to obtain the absorbed energy for each tested material at different impact energies. The results showed that the FML configuration based on a 3/4 layering arrangement (3 layers of aluminium and 4 layers of composite) exhibited the highest specific absorbed energy for the first damage and perforation threshold when compared to the other laminates and constituent materials here studied. Optical analysis showed that the plastic deformation and the tearing of the aluminium layers, as well as fibre breakage and delamination were the main impact energy-absorption mechanisms. These findings warrant further research to fully understand the low velocity impact behaviour of these thermoplastic FMLs for engineering applications.
       
  • Numerical study of low-speed impact response of sandwich panel with tube
           filled honeycomb core
    • Abstract: Publication date: Available online 5 April 2019Source: Composite StructuresAuthor(s): Jiefu Liu, Wensu Chen, Hong Hao, Zhonggang Wang Sandwich panel with Honeycomb Filled with Circular Tubes (HFCT) as core is numerically investigated by using ABAQUS/Explicit in this study. To calibrate the numerical model, the panels equipped with conventional hexagon honeycomb cores are modeled. Good agreement between numerical and experimental results is achieved. The sandwich panels with HFCT are compared with the sandwich panels with Honeycomb and Multi-tube cores of identical mass subjected to vertical and oblique impacts. The maximum displacement of face-sheets, plastic energy absorption, boundary reaction forces and impact load time history are calculated to assess the impact resistant capacity. The panel with HFCT core has smaller rear face-sheet displacement and higher energy absorption capacity as compared to the panels with the Multi-tube and Honeycomb core. Under oblique impact, both HFCT and Multi-tube panels have superior impact resistant capacity than the Honeycomb panel. In addition, the impact resistances of four types of multi-arc tube filled Honeycomb (HFMT) are also analysed. Their performances under vertical and oblique impacts are compared with those of HFCT.
       
  • Analysis and Experiment on DCB Specimen Using I-Fiber Stitching Process
    • Abstract: Publication date: Available online 5 April 2019Source: Composite StructuresAuthor(s): Jonathan Tapullima, Cheol Hwan Kim, Jin Ho Choi Several studies related to the reinforcement of composite structures in the through-thickness direction have been conducted recently. In this study, a new reinforcement process is proposed based on previous experimental results; the proposed novel process involves the stitching of T-joints and one-stitched specimens. The need for additional analysis was established under standard DCB tests, for better understanding. Finite element modeling (FEM) results were compared after performing mode I interlaminar fracture toughness tests, using different stitching patterns, for analyzing the through-thickness strength, using reference laminates without stitching. The stitching patterns were defined as 2×2 and 3×3, where the upper and lower head of the non-continuous stitching process (I-fiber) was shown to strongly affect the through-thickness strength of the laminate. To design a numerical model, cohesive parameters were required for defining surface-to-surface bonding elements using the cohesive zone method (CZM) and for simulating the crack-opening behavior from the DCB test.
       
  • Research on intralaminar load reversal damage modeling for predicting
           composite laminates’ low velocity impact responses
    • Abstract: Publication date: Available online 5 April 2019Source: Composite StructuresAuthor(s): Rui Ren, Jianlin Zhong, Guigao Le, Dawei Ma Despite abundant finite element analysis (FEA) of low velocity impact (LVI) performance of composite laminates, the questions regarding the effects of different load reversal damage laws on predicted impact responses of composite laminates and which one is preferred for more physically-sound simulation of laminate LVI responses remain unresolved. In this paper, an elasto-plastic progressive damage model based on three load reversal damage laws including coupled tension-compression law, semi-stiffness recovery law and full-stiffness recovery law, were numerically implemented in predicting laminate LVI responses. By comparisons between simulations and available experimental data, the influences of different load reversal damage laws on predicted delamination threshold load, impact force, laminate central deformation, dissipated impact energy as well as damage status were analyzed. More accurately predicting laminates’ LVI responses, the semi-stiffness recovery law was concluded as the preferred intralaminar load reversal damage law.
       
  • Horse Hoof Inspired Biomimetic Structure for Improved Damage Tolerance and
           Crack Diversion
    • Abstract: Publication date: Available online 4 April 2019Source: Composite StructuresAuthor(s): Clark Rice, K.T. Tan A biomimetic composite structure is investigated to explore the effect of angled ductile layers. The composite structure is idealized as layers of ductile material mixed with layers of hard brittle material in a rectangular bar. The layers zig zag across length of the structure with the aim to promote crack diversion. The novelty of this study is the use of such angular layers based on biomimetic inspiration from a horse hoof keratin structure. Specimens were manufactured using 3D printing technique to study the effect of different layer angles, layer thickness and crack location by single-edge notch bending test. Results showed that traditional flat thick layers provide a strong material, but zig-zagged layers are better at dispersing stress to maintain structural integrity after an impact or fatigue crack. This work provides a creative and innovative approach to design core layers in composite sandwich structures with enhanced damage tolerance.
       
  • Quasi-brittle fracture criterion of bamboo-based fiber composites in
           transverse direction based on boundary effect model
    • Abstract: Publication date: Available online 4 April 2019Source: Composite StructuresAuthor(s): Wen Liu, Ying Yu, Xiaozhi Hu, Xiangyu Han, Peng Xie Bamboo and engineered bamboo products have gathered increasing scientific and technological interests for its promising applications in sustainable engineering purpose. Bamboo-based fiber composites, a main example of engineered bamboo products, is fabricated from processing the raw bamboo bundles treated with water-soluble resin into a bamboo fiber reinforced bio-composite. The present work investigates the transverse mode-I fracture criterion of bamboo-based fiber composites: the tensile strength ft and fracture toughness KIC. The fiber bundles are taken as the “aggregates” of this material, and the average grain size G is determined as 0.4mm. By the experimental curve between the applied load and the mid-span deflection from the three-point-bending test on single edge notched specimens, the fracture process as well as the crack development includes three stages: linear, softening and failure stages. The quasi-brittle fracture criterion is calculated with the experimental peak load Pmax according to the boundary effect model in non-linear elastic fracture mechanics. Also, the normal distribution analysis is applied to cover all the experimental scatters with desired reliability. Furthermore, the method in this work on bamboo-based fiber composites can be extended to study other fiber reinforced composites.
       
  • Modeling the influence of layer shifting on the properties and nonlinear
           response of woven composites subject to continuum damage
    • Abstract: Publication date: Available online 4 April 2019Source: Composite StructuresAuthor(s): J.J. Espadas-Escalante, Brett A. Bednarcyk, Evan J. Pineda, P. Isaksson The influence of relative layer shifting on the elastic and damage response of plain weave composite laminates is analyzed using a continuum damage mechanics approach in combination with the finite element method. First, the homogenized properties of the woven composite as a function of the number of layers and of layer shifting are presented. Next, the damage development in various shifting configurations is studied using different damage constitutive models for the matrix and the fiber bundles. It is shown that the impact of layer shifting on both the elastic response and the nonlinear damage response is significant. Most notably, the model captures changes in the damage mechanisms within the woven composite that occur due to layer shifting, resulting in stiffer, more brittle behavior, which has been shown experimentally in the literature. Model results in the linear and nonlinear regimes are shown to be consistent with both an independent analytical model and reported experiments.
       
  • Characterization of deployable ultrathin composite boom for
           microsatellites excited by attitude maneuvers
    • Abstract: Publication date: Available online 3 April 2019Source: Composite StructuresAuthor(s): Susanna Laurenzi, Damiano Rufo, Marco Sabatini, Paolo Gasbarri, Giovanni B. Palmerini Composite booms are often adopted onboard spacecraft to modify inertia properties and/or to move instrument as far as possible from the influence of the platform bus. In the frame of the current trend towards smaller spacecraft, also microsatellites are increasingly equipped with these deployable appendages. Due to limited volume and mass available on these platforms, the design of the boom is more challenging and a validation of the proposed system is crucial. The paper details, from the structural dynamics point of view, the numerical and experimental validation campaign for a 1-meter boom purposely designed and built in composite material for a microsatellite platform. The experimental validation was carried out by using a free-floating platform and while simulating the loads experienced during an in-orbit attitude re-orientation maneuver. The complete architecture of the platform, including solar panels’ appendages with related flexibility issues as well as the thrusters for actuation, provides for the credibility and the interest of the validation outcome.
       
  • PSO-Driven Micromechanical Identification of In-Situ Properties of
           Fiber-Reinforced Composites
    • Abstract: Publication date: Available online 3 April 2019Source: Composite StructuresAuthor(s): Qiang Chen, Guannan Wang Within the framework of micromechanics, the newly expanded Generalized Finite-Volume Direct Averaging Micromechanics is connected to the gradient-free Particle Swarm Optimization (PSO-GFVDAM) to identify the in-situ constituent properties and residual stresses and study their effects on the effective and localized responses of fibrous composites. The present technique is advantageous by avoiding the gradient updating concept and adopting the advanced generalized finite-volume micromechanics with plasticity effects, both of which guarantee the stability and efficiency of the proposed technique. After introducing the microstructural effects from the fabrication process and chemical reaction that cannot be easily detected from the macroscopic behavior of composite materials, the PSO-GFVDAM is employed to identify the elastic constituent properties of carbon/epoxy composites, yield stress and hardening parameters of the aluminum-matrix system, as well as the residual stress state within the microstructures. The stability and accuracy of the algorithm are tested by checking the iterated particle distributions, errors generated at each step and substituting the deduced parameters back into direct analyses to predict effective responses of off-axis loaded specimens. More important to the effective response, the localized stress distributions are efficiently recovered, helping to characterize the possible damage initiation and crack propagation that usually start from the material levels.
       
  • Experimental investigation of compression and compression after impact of
           wood-based sandwich structures
    • Abstract: Publication date: 15 July 2019Source: Composite Structures, Volume 220Author(s): John Susainathan, Florent Eyma, Emmanuel De Luycker, Arthur Cantarel, Christophe Bouvet, Bruno Castanie This paper presents an experimental investigation of compression on pristine specimens and the compression after impact (CAI) response of wood-based sandwich structures. Nine different types of sandwiches, made with plywood core and different aluminum or composite (carbon or glass or flax fiber) skins, are studied. Impact energy levels were fixed at 5 J, 10 J and 15 J in order to create significant defects. Failure modes and damage scenarios are analyzed. The influence of different skins with plywood core is explained in terms of residual strength, residual stiffness, and specific properties. It is shown that this type of structure exhibits very interesting compression properties in terms of specific strength, which is superior to a reference sandwich used for aircraft flooring, and in terms of behavior, with large plateau areas that can be useful for crash issues.
       
  • Distortions of composite aerospace frames due to processing, thermal loads
           and trimming operations and an assessment from an assembly perspective
    • Abstract: Publication date: Available online 3 April 2019Source: Composite StructuresAuthor(s): Erik Kappel Composite frames in aerospace applications often show a lack of dimensional fidelity, which creates the necessity of costly shimming efforts within final assembly lines. A numerical study on C-profile frames has been performed to examine the mechanisms inducing these distortions. The paper shows that distortions are directly related to the composite’s material architecture, the part geometry and interestingly also to the state of the art zone-based frame design philosophy applied today. The paper shows that frame distortions arise from the 3D orthotropic nature of composite laminates, in-plane CTE inhomogeneity of laminate zones and coupling of different part areas. The main mechanisms inducing frame distortions are deduced from the numerical models. The paper also shows that trimming operations, which are necessary to bring frames from the manufactured to the engineered shape, significantly affect the frames’ final distortion state, the internal residual stress level as well as corresponding assembly forces during assembly.
       
  • Porosity and inhomogeneity effects on the buckling and vibration of
           double-FGM nanoplates via a quasi-3D refined theory
    • Abstract: Publication date: Available online 1 April 2019Source: Composite StructuresAuthor(s): Mohammed Sobhy, Ashraf M. Zenkour This study is devoted to illustrate the mechanical buckling and free vibration analyses of double-porous functionally graded (FG) nanoplates embedded in an elastic foundation. A new quasi-3D refined plate theory is presented to model the displacement field. This theory contains only five unknown functions and considers the shear strain as well as thickness stretching. Based on the modified Mooney-type exponential relation, a new exponential law is presented to govern the materials variation and porosities distribution through the thickness of the nanoplates. The two porous nanoplates are bonded together by a set of parallel elastic springs and surrounded by Pasternak medium. The nonlocal strain gradient theory containing the nonlocal parameter and gradient coefficient is utilized to study the size-dependent effects. Based on Hamilton’s principle, the equations of motion are drawn including the material parameters, elastic foundation reaction and biaxial compressive forces. An analytical approach for simply-supported and clamped bilayer porous FG nanoplates is implemented. The obtained results are compared with those available in the literature. Additional numerical calculations are introduced to show the influences of the material length scale parameters, inhomogeneity parameter, porosity factor and other parameters on the critical buckling and frequencies of the double-porous FG nanoplates.
       
  • Static and fatigue behavior of pultruded FRP multi-bolted joints with
           basalt FRP and hybrid steel-FRP bolts
    • Abstract: Publication date: Available online 1 April 2019Source: Composite StructuresAuthor(s): Diana S.E. Abdelkerim, Xin Wang, Haitham A. Ibrahim, Zhishen Wu This study investigates the effect of bolt types on the static and fatigue performance of basalt fiber-reinforced polymer (BFRP) multi-bolted double-lap connections. Three types of bolts are used: stainless-steel (SS), BFRP, and hybrid steel-FRP (HSFRP) bolts. Firstly, static tensile tests using steel single-bolted double-lap connections are conducted to determine the mechanical properties and failure modes of the proposed bolts. Secondly, static and fatigue tests using BFRP double-lap connections with six bolts of either SS, BFRP, or HSFRP were conducted. Finally, post-fatigue static tests were conducted to evaluate the deterioration of the composite joints caused by fatigue loading. Load-displacement curves, failure modes, fatigue life, S-N curves, and stiffness degradation are used to evaluate the effect of the bolt type on the behavior of the BFRP joints. Results indicated that SS bolts can be replaced entirely with BFRP bolts without affecting the static and fatigue performance of the joints. In addition, compared to the brittle failure of both the SS and BFRP bolts, the proposed HSFRP bolts exhibited ductile behavior which could be the key to achieving ductile composite structures. Moreover, the HSFRP bolts dramatically prolonged the fatigue life of the composite joints compared to the joints with SS and BFRP bolts.
       
  • Mechanical behavior of concrete prisms reinforced with steel and gfrp bar
           systems
    • Abstract: Publication date: Available online 1 April 2019Source: Composite StructuresAuthor(s): Arvydas Rimkus, Joaquim A.O. Barros, Viktor Gribniak, Mohammadali Rezazadeh Being immune to corrosion, and having a tensile strength up to three times higher than structural steel, glass fiber reinforced polymer (GFRP) bars are suitable for reinforcing concrete structures exposed to aggressive environmental conditions. However, a relatively low elasticity modulus of GFRP bars (in respect to the steel) favors the occurrence of relatively large deformability of cracked reinforced concrete. Lack of ductility and degradation of properties under high temperature can be also identified as debilities of GFRP bars over steel ones. Combining GFRP and steel bars can be a suitable solution to overcoming these concerns. Nevertheless, the application of such hybrid reinforcement systems requires reliable material models. The influence of the relative area of GFRP and steel bars on the tensile capacity of cracked concrete (generally known as tension-stiffening effect), was never investigated from the experimental point of view, mainly crossing results from different tools on the assessment of the cracking process. This paper experimentally investigates deformations and cracking behavior of concrete prisms reinforced with steel bars and GFRP bars in different combinations. The test results of 11 elements are reported. A tensile stress-strain diagram is conceptually proposed for modelling the tension-stiffening effect in elements with such hybrid combination of the reinforcement. The cracking process in terms of crack width and crack spacing is analyzed considering the hybrid reinforcement particularities and a preliminary approach is proposed for the prediction of the crack width for this type of reinforced concrete elements.
       
  • Damage Detection and Location in Woven Fabric CFRP Laminate Panels
    • Abstract: Publication date: Available online 28 March 2019Source: Composite StructuresAuthor(s): A. Alsaadi, J. Meredith, T. Swait, J.L. Curiel-Sosa, S. Hayes The need for multifunctional carbon fibre composite laminates has emerged to improve the reliability and safety of carbon fibre composite components and decrease costs. The development of an electrical selfsensing system for woven fabric carbon fibre composite laminate panels which can detect and locate damage due to impact events is presented. The electrical sensing system uses a four probe electrical resistance method. Two different sensing mats are investigated, the main difference between them are the surface area of the electrodes and the distance between the electrodes. To investigate the damage sensitivity of the sensing system for woven fabric carbon fibre composite laminate panels, panels are produced with various thicknesses from 0.84 3.5 mm and are impacted at 1 10 J to generate barely visible impact damage. Damage is detected using global electrical resistance changes, the changes in electrical resistance vary depending on carbon fibre volume fraction, spacing distance between the sensing electrodes in the sensing mats, the surface area of the electrodes, damage size, and damage type; it is found that the thicker the panel, the less sensitive the electrical resistance system is. The effect of the surface area of the sensing electrodes is high on the electrical resistance baseline, where the baseline increases by up to 55 % when the surface area of the sensing electrodes increases from 100mm2 to 400mm2; while spacing distance between electrodes has a greater effect on damage sensitivity of the electrical resistance sensing system than the surface area of the sensing electrodes.
       
  • A nonlocal strain gradient refined plate theory for dynamic instability of
           embedded graphene sheet including thermal effects
    • Abstract: Publication date: Available online 28 March 2019Source: Composite StructuresAuthor(s): M.H. Jalaei, Ö. Civalek In this study, nonlocal strain gradient theory (NSGT) is applied to examine the dynamic instability of embedded viscoelastic graphene sheet under periodic axial load including thermal effects. The foundation is simulated by visco-Pasternak model containing springs, dampers and a shear layer. The motion equations are derived according to the four-variable refined shear deformation plate theory and via Hamilton’s principle. The equations are converted into a linear system of Mathieu-Hill equations by means of Navier’s method. Afterwards, Bolotin’s approach is utilized to determine the principle unstable region of graphene sheet. The influences of nonlocal parameter, structural damping coefficient, length scale parameter, static load factor, temperature variation, foundation type as well as aspect ratio on the dynamic stability of graphene sheet are investigated. Based on the numerical results, it is indicated that with enlarging the nonlocal parameter, static load factor and temperature change, the excitation frequency decreases and so, instability region shifts to left side while the effect of length scale parameter is on the contrary. Additionally, it is indicated that when the length scale parameter enhances, the effects of temperature and foundation on the instability region of graphene sheet reduce.
       
  • The effect of meso-structure and surface topography on the indentation
           variability of viscoelastic composite materials
    • Abstract: Publication date: Available online 28 March 2019Source: Composite StructuresAuthor(s): Yuanqing Liu, Wenzhong Wang, Ziqiang Zhao, Haibo Zhang Most viscoelastic composites such as biomaterial, polymeric materials and silicone rubber consist of the viscoelastic matrix and the elastic inhomogeneities. Mechanical characterization of the viscoelastic composites helps us to better understand their responses under mechanical stimulation, or improve the design and manufacturing of composite products. The indentation test is the main method for measuring the mechanical properties of viscoelastic composites at present. However, the response of indentation test is sensitive to the microstructural of composites. What’s more, the surface topography also has great influence on the indentation response that cannot be ignored. In this paper, a semi-analytical method is used to model the indentation test in order to explain and improve the indentation test results. The correlation between matrix and inhomogeneity is built by the equivalent inclusion method. The conjugate gradient method and the fast Fourier transform are used to accelerate the solution of unknown variables. Based on the developed model, the effect of micro structure and surface topography on the indentation creep is investigated. The conclusions obtained from the indentation simulation agree well with the experimental results in literatures and provide solid theoretical explanation for the scatter in experimental results.
       
  • .+part+2:+monotonic+and+cyclic+sway+behaviour+of+plane+frames&rft.title=Composite+Structures&rft.issn=0263-8223&rft.date=&rft.volume=">Experimental and numerical analysis of gfrp frame structures. part 2:
           monotonic and cyclic sway behaviour of plane frames
    • Abstract: Publication date: Available online 28 March 2019Source: Composite StructuresAuthor(s): David Martins, Mário F. Sá, José A. Gonilha, João R. Correia, Nuno Silvestre, João G. Ferreira Part 1 [1] of this two-part paper presented an experimental study of the cyclic behaviour of a novel beam-to-column sleeve connection system for pultruded glass fibre reinforced polymer (GFRP) tubular profiles, and the numerical simulation of such behaviour. This Part 2 presents an experimental and numerical study on the sway behaviour of full-scale GFRP plane frames comprising the same tubular profiles and the aforementioned connection system. The GFRP frames were tested under quasi-static monotonic and cyclic loading, with and without infill walls, materialized by composite sandwich panels. The results of the tests show that high-load carrying capacity infill walls have a remarkable effect on the frames’ structural behaviour, significantly increasing their stiffness and load carrying capacity, as well as their cyclic performance, namely regarding energy dissipation. On the other hand, such improvement involved extensive damage in the frame elements, particularly in the beams, which at some point compromised their structural integrity. The numerical study included the simulation of the cyclic tests of the unfilled walls, by means of relatively simple finite element (FE) models, comprising frame elements and spring joints simulating the behaviour of the connections, in which the Pivot hysteresis model calibrated in Part 1 [1] was used. The comparison between experimental and numerical results shows that these simple and design-oriented FE models can provide an effective (and conservative) tool for the simulation of pultruded GFRP frames under horizontal cyclic loads.
       
  • Tunable wave propagation in octa-chiral lattices with local resonators
    • Abstract: Publication date: Available online 28 March 2019Source: Composite StructuresAuthor(s): Kai Zhang, Yuchao Su, Pengcheng Zhao, Zichen Deng This paper aims to investigate the wave behavior of the octa-chiral lattices with local resonators and tunable wave propagation properties with different chiral geometrical dimensions. The octa-chiral lattices are assembled with the repeat unit cells and the unit cell contains a ring and eight slender elastic massless ligaments which are rigidly connected to the ring. The ring has a heavy disk with its surrounding soft elastic annulus. The dynamic equations of the lattices are established with the principle of the Lagrangian method. The wave behaviors of the lattices are calculated by solving the eigenvalue problem governing the wave harmonic propagation with the application of the Bloch’s theorem. By calculating the band structures and the phase and group, we investigate the effects of the chiral geometry and resonators on the formation of the low-frequency band-gaps and the directional frequency-dependent energy flow. The phase and group velocities show that the maxima wave propagation speeds are along the ±45degs. While, the phase velocities and the group velocities trend to be identical with the increase of the chiral angles. The findings suggest that we can tune the anisotropic wave behavior to the isotropic wave characterization with special structural design on the chiral geometry.
       
  • Mitigating the weak impact response of thin-ply based thin laminates
           through an unsymmetrical laminate design incorporating intermediate grade
           plies
    • Abstract: Publication date: Available online 27 March 2019Source: Composite StructuresAuthor(s): A. Sasikumar, D. Trias, J. Costa, V. Singery, P. Linde With aeronautic industries focussing on thinner structures and reducing manufacturing costs, recent research has been dedicated to the impact and post impact response of thin laminates (
       
  • Mechanical Properties of Foamed Long Glass Fiber Reinforced Polyphenylene
           Sulfide Integral Sandwich Structures Manufactured by Direct Thermoplastic
           Foam Injection Molding
    • Abstract: Publication date: Available online 27 March 2019Source: Composite StructuresAuthor(s): Christoph Lohr, Björn Beck, Frank Henning, Kay André Weidenmann, Peter Elsner To achieve high levels of lightweight design in automotive or aerospace industry, it is necessary to optimize certain composite material systems concerning their lightweight potential. With sandwich composites, which generally consist of a core which is coated with two face-layers, it is possible to reduce the overall part weight while increasing the specific mechanical properties under inhomogeneously distributed loads. Hereby the sandwich core ensures the load transmission while the face layers absorb the tensile and compressive loads occurring at bending stress. The aim is to increase the efficiency of said sandwiches while minimizing the weight per area by using for example (fiber-) reinforced face layers and foamed core materials. Polyphenylene sulfide (PPS) is an important high temperature, engineering thermoplastic polymer. Because of its properties it is used in the automotive, aerospace and electronics industry. As polyphenylene sulfide has a high processing temperature and requires processing know-how, there a few scientific studies on its foaming behavior. To understand the process-structure-property relationship of this material system, an experimental study on the foaming behavior of neat polyphenylene sulfide and long glass fiber reinforced polyphenylene sulfide using the high-pressure foam injection molding process is conducted. As it is also attractive from a manufacturing point of view to reduce the number of manufacturing steps and to operate with the source materials from the beginning of the process an in-line compounding and foam injection molding process is used. This allows the manufacturing of integral sandwich structures with connected, fiber reinforced face and foamed core layers in one shot via “direct thermoplastic foam injection molding”. With the findings of this study researchers and manufacturers of neat and fiber reinforced PPS parts are able to identify process parameter boundaries and the influence of these parameters on the sandwich structure and mechanical properties.
       
  • A study of energy dissipating mechanisms in orthogonal cutting of UD-CFRP
           composites
    • Abstract: Publication date: Available online 27 March 2019Source: Composite StructuresAuthor(s): Xiaoye Yan, Johannes Reiner, Mattia Bacca, Yusuf Altintas, Reza Vaziri This paper presents a three-dimensional thermo-mechanical finite element (FE) model on the micro-scale for the orthogonal cutting simulation of unidirectional carbon fiber reinforced polymer (UD-CFRP) materials. Fiber, matrix and the fiber-matrix interface are modeled separately to simulate failure mechanisms associated with fiber breakage, matrix cracking and fiber-matrix debonding. Experiments on orthogonal cutting of UD-CFRP workpieces with various fiber orientations have been conducted and compared to the micro-scale FE simulations. The good correlation between the experimental and numerical results with respect to cutting forces, chip formation and surface quality enables for an in-depth FE energy analysis to quantify dominating failure mechanisms in different fiber orientations. In addition, the contribution of each fiber failure mode during orthogonal cutting is evaluated. It is found that dissipated energies associated with various failure modes and friction vary with the fiber orientations and that the simulation provides insight into the characteristic fiber orientation-dependent quantities observed in the experiments such as chip formation and surface morphology. Finally, a sensitivity analysis is carried out to assess the variation of the simulated cutting response with respect to input parameters with high uncertainty including friction coefficients or fiber strength values.
       
  • Experimental and numerical analysis of gfrp frame structures. part 1:
           cyclic behaviour at the connection level
    • Abstract: Publication date: Available online 27 March 2019Source: Composite StructuresAuthor(s): David Martins, Miguel Proença, José A. Gonilha, Mário F. Sá, João R. Correia, Nuno Silvestre Pultruded glass fibre reinforced polymer (GFRP) profiles have low weight, high strength and corrosion resistance, but their brittle failure raises concerns about their use in seismic regions. Moreover, although their static monotonic response is reasonably well understood, the cyclic and hysteretic behaviour of GFRP frame structures and their beam-to-column connections have not yet been comprehensively investigated. This paper presents experimental and numerical investigations on the cyclic behaviour of a novel tubular GFRP beam-to-column sleeve connection system, comprising internal metallic parts. Four series of the connection system were tested, with varying number and position of the beam connection bolts, namely with: (i) one bolt in the webs (W1); (ii) two bolts in the flanges (F2); (iii) four bolts in the flanges (F4); and (iv) two bolts in the flanges with larger edge distance (F2S). The results show that series W1 presents the worst overall cyclic behaviour. On the other hand, the addition of bolt rows (F4 vs. F2) did not improve the cyclic response of the connection system. Conversely, increasing the edge distance (F2S vs. F2) led to significant improvements of the hysteretic behaviour, namely in the capacity to dissipate energy. Using the Pivot hysteresis model in the numerical study, a design-oriented model comprising frame and link elements was developed to simulate the response of the best performing series (F2S). In spite of its simplicity, the numerical simulation provided good agreement with the experimental results. In a companion paper, the behaviour of full-scale frames comprising F2S connections under monotonic and cyclic quasi-static sway tests was experimentally assessed. Numerical models of these tests were also developed to simulate the cyclic behaviour of the frames, using the parameters of the Pivot hysteresis model calibrated herein.
       
  • Deformation and damage of liquid-filled cylindrical shell composite
           structures subjected to repeated explosion loads: experimental and
           numerical study
    • Abstract: Publication date: Available online 27 March 2019Source: Composite StructuresAuthor(s): Liangyu Cheng, Chong Ji, Fuyin Gao, Yang Yu, Yuan Long, You Zhou The dynamic response and structural damage of liquid-filled cylindrical shell composite structures, with different wall thicknesses and at varying stand-off distances, under repeated explosion loading were studied experimentally. The explosion resistance of liquid-filled cylindrical shell composite structures influenced by the wall thickness and stand-off distances was clarified, and the resistance thickness and critical distance were determined. The effect of internal liquid filling enhance the ability of the cylindrical shell to resist explosion loading was verified by experimental data. A stronger explosive load and greater deformation result in a more obvious enhancement effect of liquid filling on the cylindrical shell structure.The deformation and damage results of the liquid-filled cylindrical shell composite structures were divided into five typical modes. Three major modes were analysed numerically. By means of numerical simulation, the deformation and damage processes of the liquid-filled cylindrical shell composite structures subjected to repeated explosive loading were studied. The energy transformation directions of the three major modes were investigated in their respective deformation processes.
       
  • 2D Underwater Acoustic Metamaterials Incorporating a Combination of
           Particle-filled polyurethane and Spiral-based Local Resonance Mechanisms
    • Abstract: Publication date: Available online 26 March 2019Source: Composite StructuresAuthor(s): Haibin Zhong, Yinghong Gu, Bin Bao, Quan Wang, Jiuhui Wu This paper develops an underwater acoustic metamaterial plate with potential advantages of low-frequency broadband sound absorption and high hydrostatic pressure resistance. In this research, a new acoustic metamaterial embedding particle-filled polyurethane (PU) and spiral-based local resonance mechanism for underwater sound absorption is investigated numerically and experimentally. Specifically, the proposed metamaterial is composed of particle-filled PU damping materials and a square lattice of spiral resonators. The thickness of the proposed plate structure occupying most of the area is thin and equals to 4 mm. Wave propagation properties of the proposed metamaterial are obtained by using the finite element (FE) method. Compared to the underwater sound absorption coefficient, the formation mechanisms of the locally resonant band gaps are investigated based on the modal analysis of plate modes and local resonances. Results show that the location and bandwidth of newly generated locally low-frequency resonant band gaps are greatly affected by the interaction between particle-filled PU and the spiral resonator within every periodic cell. In addition, the theoretical results of the underwater sound absorption coefficient of the proposed metamaterial are compared with the experimental results. In the frequency domain [0.8kHz, 6kHz], the average sound absorption coefficient of the proposed metamaterial plate under normal atmospheric pressure is 0.54. Furthermore, the sound absorption coefficient of the proposed structure is experimentally studied under different hydrostatic pressure conditions. Specifically, the proposed metamaterial structure achieves average sound absorption coefficient of 0.51 in the frequency range [1.5kHz,6kHz] under 0.5MPa.
       
  • A generic non-linear bond-slip model for CFRP composites bonded to
           concrete substrate using EBR and EBROG techniques
    • Abstract: Publication date: Available online 26 March 2019Source: Composite StructuresAuthor(s): Mohsen Heydari Mofrad, Davood Mostofinejad, Ardalan Hosseini In this study, a generic bond-slip model is proposed for carbon fiber reinforced polymer (CFRP) reinforcement bonded to concrete substrate. The model is applicable to concrete members strengthened by the conventional externally bonded reinforcement (EBR) technique, as well as to those members strengthened using the recently introduced externally bonded reinforcement on grooves (EBROG) method. The model was first calibrated using 32 single lap-shear tests performed on EBR and EBROG joints having various concrete strength, CFRP thickness, and groove depth (in case of EBROG joints). Afterwards, the excellent performance of the model in terms of its high prediction accuracy of the bond-slip behavior and ultimate capacity of EBR and EBROG joints was verified using a set of independent experimental data collected from the existing literature. Owing to the certain advantages of the proposed model including its high accuracy and applicability to predict the bond behavior and strength of both EBR and EBROG joints, the proposed model can be an efficient alternative to the existing ones for predicting the CFRP-to-concrete bond behavior. Furthermore, single lap-shear tests performed on CFRP strips bonded to concrete substrates demonstrated that the interfacial fracture energy of EBROG joints is almost three times that of the EBR joints.
       
  • Multi-objective robust design optimization of a two-dimensional tri-axial
           braided hollow pillar using an evolutionary algorithm
    • Abstract: Publication date: Available online 26 March 2019Source: Composite StructuresAuthor(s): Jishi Yang, Dongyang Sun, Ning Hu, Huiming Ning, Jianyu Zhang, Wei Ye, Jian Wu In this work, multi-objective robust optimization of a two-dimensional tri-axial braided hollow pillar was presented. Two conflicting objectives, weight and cost, were simultaneously minimized under the constraint of mechanical safety requirements based on Probability theory. The material properties were taken into account with three design variables and two uncontrollable variables. The three design variables were the total fiber volume fraction, the relative volume fraction of carbon fiber in the total fiber volume fraction and the braid angle. The two uncontrollable variables were the fiber volume fraction of the carbon fiber tows and of the glass fiber tows. A mesoscopic analytical model of the two-dimensional tri-axial braided composites (2DTBC) was adopted to obtain the necessary mechanical parameters. Appropriate surrogate models were used to investigate the approximate relationship between the mechanical properties and the input variables, which could significantly reduce the calculation cost. The optimization problem was solved with Pareto optimal solutions through a multi-objective evolutionary solver. The results indicate that, in general, the uncertainty in the total fiber volume fraction was the main decisive factor in the robust optimization and mechanical analysis of the monolithic construction.
       
  • Sound transmission loss of laminated composite sandwich structures with
           pyramidal truss cores
    • Abstract: Publication date: Available online 26 March 2019Source: Composite StructuresAuthor(s): Dong-Wei Wang, Li Ma, Xin-Tao Wang, Zhi-Hui Wen, Christ Glorieux This paper presents a theoretical model that allows to calculate the acoustic transmission loss through laminated composite pyramidal sandwich structure consisting of two parallel plates connected by trusses. First-order shear deformation theory is adopted to model the vibration of such a structure, accounting for in-plane motion and coupling between extension and flexure of the different components, and taking into account elastic anisotropy. The interaction between the structure and the surrounding fluid is taken into account by imposing a velocity continuity condition at the interfaces. The displacement and stress fields are calculated in Fourier domain by solving the set of boundary condition equations at the connecting points. The theoretical predictions for the acoustic transmission through the structure show satisfactory agreement with experimental results of a standing wave tube experiment on specimens that were fabricated by cutting trusses from carbon fiber reinforced composite plates and snap-fitting them to plates made of the same material. Numerical simulations are used to verify, the influence of the stacking geometry and material parameters on the acoustic transmission for different frequencies and angles of incidence. Conclusions are presented that are helpful for practical design.
       
  • Thermal and Mechanical Properties of Carbon Fiber-Reinforced Resin
           Composites with Copper/Boron Nitride Coating
    • Abstract: Publication date: Available online 26 March 2019Source: Composite StructuresAuthor(s): Xiru Zheng, Chan Woo Park Copper and hexagonal boron nitride filler (Cu/hBN) were incorporated into carbon fiber-reinforced polymer (CFRP) composites by electrophoretic deposition (EPD) to maximize their thermal conductivity. The results show that the thermal conductivity increased to 1.68 and 5.15 W/mK in the through-thickness and in-plane directions, respectively, when the concentration of hBN particles in the deposition solution was increased to 5 g/L. Moreover, the interlaminar shear strength results of various composites exhibited the same trend as the thermal conductivity. However, the tensile test results showed that the tensile strength was reduced as the hBN concentration was increased.
       
  • Buckling and free vibrations of rectangular plates with symmetrically
           varying mechanical properties – analytical and FEM studies
    • Abstract: Publication date: Available online 26 March 2019Source: Composite StructuresAuthor(s): Krzysztof Magnucki, Dawid Witkowski, Ewa Magnucka-Blandzi The subject of the paper is a rectangular plate with symmetrically varying mechanical properties in the thickness direction. The nonlinear hypothesis of deformation of the straight line normal to the plate neutral surface is assumed. The field of displacements of the plate is formulated assuming this hypothesis. Based on the Hamilton’s principle three differential equations of motion are obtained. The system of equations is analytically solved. The critical loads and fundamental natural frequencies for exemplary plates are derived. Moreover, the FEM model of the plate in the ABAQUS system is developed, and analogical calculations for exemplary plates are carried out. The calculation results of these two methods are compared.
       
  • Study of the Fracturing Behavior of Thermoset Polymer Nanocomposites via
           Cohesive Zone Modeling
    • Abstract: Publication date: Available online 26 March 2019Source: Composite StructuresAuthor(s): Yao Qiao, Marco Salviato This work proposes an investigation of the fracturing behavior of polymer nanocomposites. Towards this end, the study leverages the analysis of a large bulk of fracture tests from the literature with the goal of critically investigating the effects of the nonlinear Fracture Process Zone (FPZ).It is shown that for most of the fracture tests the effects of the nonlinear FPZ are not negligible, leading to significant deviations from Linear Elastic Fracture Mechanics (LEFM) sometimes exceeding 150% depending on the specimen size and nanofiller content.To get a deeper understanding of the characteristics of the FPZ, fracture tests on geometrically-scaled Single Edge Notch Bending (SENB) specimens are analyzed leveraging a cohesive zone model. It is found that the FPZ cannot be neglected and a bi-linear cohesive crack law generally provides the best match of the experimental data.
       
  • The strain performance of thin CFRP-SPCC hybrid laminates for automobile
           structures
    • Abstract: Publication date: Available online 26 March 2019Source: Composite StructuresAuthor(s): Muhammad Akhsin Muflikhun, Tomohiro Yokozeki, Takahira Aoki In this study, the strain performances of CFRP-SPCC hybrid laminates are investigated. The quasi-static tensile test and Classical Lamination Theory (CLT) was used and compared to evaluate strain performance of hybrid laminates consisting of 0°, 45°, -45°, and 90° plies and SPCC plate. The experimental results show a maximum strain of 1.85% at the maximum stress for [0]4 and 2.15% for [SPCC/±45/0]S hybrid laminates. The hybrid laminates have shown that adding SPCC to CFRP laminates can increase the performance of the laminates by delaying the failure for more than 16% in terms of strain. The different failure modes of the laminates after tests are observed and evaluated considering the residual thermal strains and stresses.
       
  • Defect Detection of Composite Adhesive Joints Using Electrical Resistance
           Method
    • Abstract: Publication date: Available online 26 March 2019Source: Composite StructuresAuthor(s): So-Jung Baek, Man-Sung Kim, Woo-Jin An, Jin-Ho Choi Mechanical joint and adhesive bonding are two typical joining methods for composite materials. The bolt fastening method is reliable but increases the weight of the structure and cuts the composite fiber, which may cause stress concentration and strength degradation. The adhesive bonding method has a higher bonding strength than the mechanical fastening, but the bonding strength can deteriorate depending on the various parameters that influence the environmental conditions and manufacturing process. In addition, bonding defects due to the presence of foreign substances on the bonding surface or immature surface treatment is called a Kissing Bond, and can significantly reduce the bonding strength. The electrical resistance method is a very promising technique for detecting kissing bond defects by measuring the electrical characteristics after the dispersion of CNTs in the adhesive.In this study, composite-to-composite single-lap joint specimens with CNTs were fabricated and the defect detection capability and the static strength of composite joints were evaluated using the electrical resistance method. A carbon/epoxy composite was used as an adherend and the electrical resistance of the adhesive joint was measured by varying the content of CNTs to 0.5 wt%, 1.0 wt%, and 2.0 wt%. The AC and DC resistance values of composite adhesive joints with artificial defects were measured using an LCR meter and a high-resistance meter, and their lap shear strengths were evaluated.
       
  • On the effect of glass and carbon fiber hybridization in fiber metal
           laminates: Analytical, numerical and experimental investigation
    • Abstract: Publication date: Available online 23 March 2019Source: Composite StructuresAuthor(s): Konrad Dadej, Jaroslaw Bienias, Barbara Surowska In the classical composites, the hybridization of carbon and glass fibers may cause a positive hybrid effect, which relies on the increase of carbon fibers failure strain, when compared to the pure carbon-based composites. This paper focuses on the investigation of the influence of the volume ratio of carbon and glass fibers hybridization in Fiber Metal Laminates, on the static tensile strain at which the laminate fails. Analytical, numerical and experimental studies have proven that the increase of carbon fibers failure strain occurs in the Fiber Metal Laminates and can be explained by the presence of thermal stresses caused by the manufacturing process at elevated temperature.
       
  • Bayesian Identification of Mean-Field Homogenization model parameters and
           uncertain matrix behavior in non-aligned short fiber composites
    • Abstract: Publication date: Available online 23 March 2019Source: Composite StructuresAuthor(s): Mohamed Mohamedou, Kepa Zulueta Uriondo, Chi Nghia Chung, Hussein Rappel, Lars Beex, Laurent Adam, Aitor Arriaga, Zoltan Major, Ling Wu, Ludovic Noels We present a stochastic approach combining Bayesian Inference (BI) with homogenization theories in order to identify, on the one hand, the parameters inherent to the model assumptions and, on the other hand, the composite material constituents behaviors, including their variability. In particular, we characterize the model parameters of a Mean-Field Homogenization (MFH) model and the elastic matrix behavior, including the inherent dispersion in its Young’s modulus, of non-aligned Short Fibers Reinforced Polymer (SFRP) composites. The inference is achieved by considering as observations experimental tests conducted at the SFRP composite coupons level. The inferred model and material law parameters can in turn be used in Mean-Field Homogenization (MFH)-based multi-scale simulations and can predict the confidence range of the composite material responses.
       
  • Bond behaviour between CFRP plates and corroded steel plates
    • Abstract: Publication date: Available online 22 March 2019Source: Composite StructuresAuthor(s): Anbang Li, Shanhua Xu, Hao Wang, Huifeng Zhang, Yan Wang The purpose of this study is to investigate the bond behaviour between CFRP plates and corroded steel plates. Double-lap joint specimens with six kinds of corrosion duration and four kinds of adhesive thickness were tested and the primary bond characteristics were analyzed together with the effect of corrosion duration on the surface characteristic. Results showed that the failure mode of the specimens mainly depended on adhesive thickness rather than corrosion duration, only when the adhesive layer take a critical thickness, the failure modes would be significantly affected by corrosion duration, furthermore, corrosion was found to have a positive effect on the ultimate load for the specimens with the same failure mode of steel/adhesive interfacial failure, and the effective bond length of the corroded specimens were obviously larger than that of the un-corroded ones. Results also indicated that as for the specimens of the same corrosion duration, the failure modes changed from the combination of steel/adhesive interfacial failure and CFRP/adhesive interfacial failure to the combination of CFRP/adhesive interfacial failure and CFRP delamination, the ultimate load increased at first and decreased afterwards, and the effective bond length progressively increased with the adhesive thickness increased from 0.5 to 1.0, 1.5 and 2.0 mm.
       
  • Local Buckling Analysis of Periodic Sinusoidal Corrugated Composite Panels
           under Uniaxial Compression
    • Abstract: Publication date: Available online 19 March 2019Source: Composite StructuresAuthor(s): Sachinthani Pathirana, Pizhong Qiao The critical local buckling of simply-supported sinusoidal panels subjected to uniaxial compression using the Rayleigh-Ritz method is investigated. With increased applications of thin-walled composite structures in engineering, these corrugated panels are especially popular due to their high stiffness to weight ratio and high out-of-plane rigidities. Failure of such thin-walled panels occurs mainly in buckling rather than material failure; thus, it leads to importance of buckling failure analysis. Conventional methods are limited when analyzing these panels in local buckling because of its unique geometries. Hence, a semi-analytical solution is developed to predict the local buckling based on classical shell theory with a unit cell approach, and it shows excellent correlation with the results based on the numerical finite element analysis. A parametric study is conducted to evaluate the effects of the thickness, aspect ratio, and the corrugated amplitude of the panel on buckling. It is revealed that the derived solution can accurately capture the local buckling behavior at high thickness/radius of curvature ratios, any aspect ratios, and high corrugated amplitudes. Additionally, the effects of orthotropy, Poisson’s ratios and twisting capacities on the buckling behavior are explored. The proposed semi-analytical solution can be effectively used to aid in the efficient and accurate design analysis and optimization of corrugated panels.
       
  • Application of plate decomposition technique in nonlinear and
           post-buckling analysis of functionally graded plates containing crack
    • Abstract: Publication date: Available online 13 March 2019Source: Composite StructuresAuthor(s): S.A.M. Ghannadpour, M. Karimi, F. Tornabene Nonlinear and post-buckling behaviors of internally cracked functionally graded plates subjected to uniaxial compressive loading have been presented in this paper. A general nonlinear mathematical model for cracked functionally graded plates has been developed based on the first order shear deformation theory within the framework of von-Karman nonlinearity. To approximate the primary variables, Legendre polynomials are used in the current research. The crack is modelled by decomposing the entire domain of the plate into several sub-plates and therefore, a plate decomposition technique is applied. In this study, the penalty technique is used to enforce interface continuity between the sub-plates. The integrals of the potential energy are numerically computed by Gauss-Lobatto quadrature formulas to get adequate accuracy. Finally, the obtained non-linear system of equations is solved by the well-known Newton-Raphson technique. Results are presented to show the influence of crack length, various locations of crack, crack direction, boundary conditions and volume fraction index in nonlinear behavior of functionally graded plates.
       
  • A composite metamaterial with sign switchable elastic and hygrothermal
           
    • Abstract: Publication date: Available online 11 March 2019Source: Composite StructuresAuthor(s): Teik-Cheng Lim The negativity of material properties has opened up the possibility for the design of materials and structures that can perform in ways that are not achievable by conventional ones. Yet, conventional materials still possess their merits in certain applications. This paper explores a class of triangular-based composite metamaterial microstructure, with pin joints, that exhibits positive and negative Poisson’s ratio as a result of tensile and compressive loads respectively. By incorporating an additional set of rods, the modified microstructure behaves as a positive hygrothermal expansion material due to decrease in temperature and/or moisture concentration, but exhibits negative hygrothermal expansivity upon the increase of temperature and/or moisture concentration. The possibility of producing materials with behavioral multiplicity offers opportunities for development of materials and structures that reverse their behavior depending on the switch in stress sign as well as a switch in the sign for change(s) to the environmental temperature and/or moisture concentration.
       
  • Behavior of FRP-Confined High-Strength Concrete under Eccentric
           Compression: Tests on Concrete-Filled FRP Tube Columns
    • Abstract: Publication date: Available online 7 March 2019Source: Composite StructuresAuthor(s): Ali Fallah Pour, Aliakbar Gholampour, Junai Zheng, Togay Ozbakkaloglu Accurate modeling of the complete stress-strain relationship of confined concrete is of vital importance in predicting the structural behavior of confined concrete columns under combined axial compression and bending. Although the axial stress-strain behavior of confined concrete under concentric loading is well established, the behavior under eccentric loading when axial and bending loads are combined is not well understood. This paper presents an experimental study on the behavior of carbon fiber-reinforced polymer (FRP)-confined high-strength concrete (HSC) columns under eccentric compression loading. 31 short concrete columns with circular and square cross-sections were tested under compression with different load eccentricities. The equivalent axial stress-strain curves of FRP-confined HSC under eccentric loading are obtained through sectional analysis conducted on the recorded experimental data. The results indicate that load eccentricity significantly affects the axial stress-strain behavior of FRP-confined HSC. In both circular and square cross-section specimens, an increase in the load eccentricity results in an increase in the ultimate axial strain but a decrease in the second branch slope of the axial stress-strain curve, which translated to a reduced ultimate axial stress in the specimens of the current study. The analysis of the results have shown that the ultimate axial strain increased and ultimate axial stress and second branch slope of the axial stress-strain curve decreased almost linearly with increasing eccentricity.
       
  • Decision Tree-based Machine Learning to Optimize the Laminate Stacking of
           Composite Cylinders for Maximum Buckling Load and Minimum Imperfection
           Sensitivity
    • Abstract: Publication date: Available online 2 March 2019Source: Composite StructuresAuthor(s): H.N.R. Wagner, H. Köke, S. Dähne, S. Niemann, C. Hühne, R. Khakimova Launch-vehicle primary structures like cylindrical shells are increasingly being built as monolithic composite and sandwich composite shells. These imperfection sensitive shells are subjected to axial compression due to the weight of the upper structural elements and tend to buckle under axial compression. In the case of composite shells the buckling load and imperfection sensitivity depend on the laminate stacking sequence.Within this paper multi-objective optimizations for the laminate stacking sequence of composite cylinder under axial compression are performed. The optimization is based on different geometric imperfection types and a brute force approach for three different ply angles. Decision tree-based machine learning is applied to derive general design recommendations which lead to maximum buckling load and a minimum imperfection sensitivity.The design recommendation are based on the relative membrane, bending, in-plane shear and twisting stiffnesses. Several optimal laminate stacking sequences are generated and compared with similar laminate configurations from literature. The results show that the design recommendations of this article lead to high-performance cylinders which outperform comparable composite shells considerably. The results of this article may be the basis for future lightweight design of sandwich and monolithic composite cylinders of modern launch-vehicle primary structures.
       
 
 
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